Thundereggs!

[1dave]

Jul 14, 2020 21:06:52 GMT -7 @rwa3006 said:

Jul 14, 2020 20:12:14 GMT -7 knave said:

Ok. Richardson’s Ranch has the distinctive star patterns on the inside.
What, if any, are the theories why it is such a local feature?

I can't remember where, but 1dave has presented some really good information on this topic.

One place was:
forum.rocktumblinghobby.com/post/748167/thread

Richardson Ranch is on part of the John Day Formation.

At "the ranch," as the hot water turned to steam, the spheroids tended to break into more or less internal six sided box shapes.

  From the colorful minerals inside, I'd say this specimen was from the "Priday Ranch" layer (eruption).

Basics are that Si-O² structures change with temperature and pressure. (AND the presence of other elements)

Heating up from Zero to 10,000, first the core of one element will increase vibrating to the point where the "Forbidden Zone" will increase to the point where the electrons are forced to move out to the next path; then the other will soon follow suit. this increases their sizes

- Quantum Mechanics -.

This is a predictable and repeatable path, occurring at precise temperatures and pressures.

Increasing from room temperature: SiO² gel > opal > needles > spheroids > chalcedony > moganite > alpha quartz > beta quartz > 7 forms of tridymite > 2 forms of cristobalite > spheroids > liquid > gas > plasma.

Cooling Down is a different matter.

External Structure tends to hold on to shape, sometimes obvious as "crazing" as b quartz cools below 575^oC into a quartz.

Most volcanoes are subduction volcanoes with a life span of only several thousand years. Not time enough to grow very large spheroids.

Spheroids in Utah obsidian.

HOT-SPOT VOLCANOES are a very different matter! They live for many millions of years. The longer they go between eruptions, the more time to add new layers to each spheroid, adding to ever larger spheroid and ultimate thunderegg size at that location.

Siletzia Large Thundereggs are found all along it's track.

60 Ma the Siletz hotspot suddenly appeared off the west coast of America. From a depth of perhaps 200 - 600 miles superheated mantle material began welling up, spewing basalt that became the huge Siletzia Seamount.
For the next 10 ma Siletzia became massive, around 10,000 cubic miles of basalt - about the size of Hawaii!!

This crashed into the Washington/Oregon coast ~50 Ma. As the hotspot moved under the continent, it began melting and spewing limestone from the continental shelf, then as the continent moved over it, silica rocks. (I think it was an extremely high speed - perhaps 1/8th the speed of light from a nearby supernova ? - asteroid impact)

From Siletzia to Yellowstone

Age Name State Volume
57-50 Ma Siletzia Oregon 10,000 Cu. Mi.
54-39 Ma Tillamook Oregon
41-25 Ma Wildcat Mt. Oregon
29 Ma Smith Rock Oregon

13-10 Ma Crooked River Oregon
16-15.1 Ma McDermitt Oregon/Idaho
13.8-12 Ma Oyhee-Humbolt Oregon/Idaho
12.5-11.3 Ma Bruneau-Jarbidge Oregon/Idaho
10-8.6 Ma Twin Falls Idaho
10.2 Ma Picabo Idaho
7 Ma Rattlesnake Tuff Oregon
6.6-4.4 Ma Heise Idaho
2-0.6 Ma Yellowstone Idaho.Wyoning

The original Siletzia basalts are tholeiitic, a characteristic of mantle-derived magma erupted from a spreading ridge between plates of oceanic crust. The younger basalts are alkalic or calc-alkaline, characteristic of magmas derived from a subduction zone. This change of composition reflects a change from marine to continental volcanism that becomes evident around 48 to 42 Ma (millions of years ago), and is attributed to the accretion of Siletzia to the North American continent.


OREGON
1. Siletzia Washington/Oregon - (58-50 Ma) - tholeiitic basalts turn to alkalic or calc-alkaline basalts.

2. Tillamoock Oregon Caldera - (54 to 39 Ma) - calc-alkaline basalts turn to silicates.

The older Clarno Formation consists of Eocene non-marine alkaline to calk-alkaline volcanic rocks and intrusions and volcanogenic sedimentary rocks that reputedly range in age from ca. 54 to 39 Ma

3. Wildcat Mt. Caldera - (41-25 Ma) - John Day Formation - first Thundereggs - Madras, Richardson Ranch, Lucky Strike Mine

Robinson and Brem (1981) divided the John Day Formation into a “western”, “southern”, and “eastern” facies (Figure 1). The “western” facies is divided into members designated alphabetically from A to I (Figure 4; Peck, 1964; Robinson and Brem, 1981; Robinson and others, 1990). The “eastern” facies is divided into four members that include from oldest to youngest the Big Basin, Turtle Cove, Kimberly, and Haystack Valley members (Fisher and Rensberger, 1972). The “southern” facies has not been formally divided into members. The base of the John Day Formation is generally defined by the regionally widespread Member A ash-flow tuff that has 40Ar/39Ar ages of 39.72 ± 0.03 Ma near the Painted Hills, 39.22 ± 0.03 Ma near Clarno, and 39.17 ± 0.15 Ma near Ashwood (Bestland and Retallack, 1994a,b; Smith and others, 1998; Retallack and others, 2000). An ash flow defined as Member I near the top of the formation has been dated at 27.7 ± 0.3 Ma (K/Ar) but may be as young as 22 Ma

Mercury from the impact began reaching the surface in the 39 Ma eruptions.
Intermediate to silicic basement rocks and rocks associated with the Wildcat Mountain caldera are characterized by relatively enriched amounts of Al (aluminum) and corresponding relatively depleted contents of K (potassium), Na (sodium), and Fe (iron). These rocks also display characteristically low contents of incompatible high-field-strength elements (HFSE) such as Nb (niobium) and Zr (zirconium), low contents of Y (yttrium), and, generally, lower abundances of the light rare-earth elements (LREE) La (lanthanum) and Ce (cerium)

Oligocene Crooked River caldera
10–13 Ma younger Lower Crooked volcanic field rocks. Mafic rocks preserved within the Lower Crooked volcanic field are Fe- and Ti-rich tholeiites while silicic rocks are characterized by relatively enriched amounts of Y, Zr, Nb, La, and Ce

?. Smith Rock Caldera, Bend Oregon - 29 Ma
The geology of Smith Rocks is volcanic. It is made up of layers of recent basalt flows overlaying older Clarno ash and tuff formations. Approximately 30 million years ago, a large caldera was formed when overlying rock collapsed into an underground lava chamber. This created a huge amount of rock and ash debris that filled the caldera. That material solidified into rock, becoming Smith Rock tuff. Rhyolite flows intruded along faults in the Smith Rock Tuff. [2] A half million years ago, basalt lava flows from nearby volcanoes covered the older tuff.[3][4][5]

More recently, the Crooked River cut its way through the layers of rock to create today's geographic features. Smith Rock itself is a 3,200-foot (980 m)-high ridge (above sea level) with a sheer cliff-face overlooking a bend in the Crooked River (elev. 2600 ft), making the cliffs about 600 feet high.

Tower Mountain Caldera


OREGON/NEVADA
McDermitt Caldera (16-15.1 Ma)

OREGON/NEVADA/IDAHO
Owyhee-Humboldt Caldera (13.8-12 Ma)

NEVADA/IDAHO
Bruneau-Jarbidge Caldera (12.5-11.3 Ma) Bruneau Thundereggs

IDAHO
Twin Falls Caldera (10-8.6 Ma)
Picabo Caldera (10.2 Ma)
Heise Caldera (6.6-4.4 Ma) V

IDAHO/MONTANA/WYOMING
Yellowstone Caldera (2-0.6 Ma)

The LARGEST Spheroids I know of are at Silver Cliff Colorado, near @nrg Scott Solar's new home.

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Recently @woodman posted this photo on RTH:

  From the colorful minerals inside, I'd say this specimen was from the "Priday Ranch" layer (eruption).

Richardson Ranch is on part of the John Day Formation.

Long ago I posted:
forum.rocktumblinghobby.com/post/748167/thread

Native Americans of the Pacific Northwest saw mountains go to war and fling fiery rocks at each other. When they found this kind of rocks near them they assumed they were the "Thundereggs" thet had seen flying through the air.



Basics are that Si-O² structures change with temperature and pressure. (AND the presence of other elements)

Heating up from Zero to 10,000, first the core of one element will increase vibrating to the point where the "Forbidden Zone" will increase to the point where the electrons are forced to move out to the next path; then the other will soon follow suit. this increases their sizes

- Quantum Mechanics -.

This is a predictable and repeatable path, occurring at precise temperatures and pressures.

Increasing from room temperature: SiO² gel > opal > tridymite > needles > spheroids > chalcedony > moganite > alpha quartz > beta quartz > there are 7 forms of this one) tridymite > (2 forms of) cristobalite > spheroids > liquid > gas > plasma.

Cooling Down is a different matter.

External Structure tends to hold on to shape, sometimes obvious as "crazing" as b quartz cools below 575^oC into a quartz.

Most volcanoes are subduction volcanoes with a life span of only several thousand years. Not time enough to grow very large spheroids.

Hot water under intense pressure is trapped between the needles.
As the encasing lava (Rhyolite or Obsidian - the surface form of granite) slowly cools down and contracts, it allows the hot water to turn into steam. That slow "
explosion" forces the ruptured openings that are long afterward filled with materials deposited by invading mineralized ground waters.

Spheroids in Utah obsidian.

HOT-SPOT VOLCANOES are a very different matter! They live for many millions of years. The longer they go between eruptions, the more time to add new layers to each spheroid, adding to ever larger spheroid and ultimate thunderegg size at that location.

Siletzia Large Thundereggs are found all along it's track.

60 Ma the Siletz hotspot suddenly appeared off the west coast of America. From a depth of perhaps 200 - 600 miles superheated mantle material began welling up, spewing basalt that became the huge Siletzia Seamount.
For the next 10 ma Siletzia became massive, around 10,000 cubic miles of basalt - about the size of Hawaii!!

This crashed into the Washington/Oregon coast ~50 Ma. As the hotspot moved under the continent, it began melting and spewing limestone from the continental shelf, then as the continent moved over it, silica rocks. (I think it was an extremely high speed - perhaps 1/8th the speed of light from a nearby supernova ? - asteroid impact)

From Siletzia to Yellowstone

Age Name State Volume
57-50 Ma Siletzia Oregon 10,000 Cu. Mi.
54-39 Ma Tillamook Oregon
41-25 Ma Wildcat Mt. Oregon
29 Ma Smith Rock Oregon

13-10 Ma Crooked River Oregon
16-15.1 Ma McDermitt Oregon/Idaho
13.8-12 Ma Oyhee-Humbolt Oregon/Idaho
12.5-11.3 Ma Bruneau-Jarbidge Oregon/Idaho
10-8.6 Ma Twin Falls Idaho
10.2 Ma Picabo Idaho
7 Ma Rattlesnake Tuff Oregon
6.6-4.4 Ma Heise Idaho
2-0.6 Ma Yellowstone Idaho.Wyoning

The original Siletzia basalts are tholeiitic, a characteristic of mantle-derived magma erupted from a spreading ridge between plates of oceanic crust. The younger basalts are alkalic or calc-alkaline, characteristic of magmas derived from a subduction zone. This change of composition reflects a change from marine to continental volcanism that becomes evident around 48 to 42 Ma (millions of years ago), and is attributed to the accretion of Siletzia to the North American continent.


OREGON
1. Siletzia Washington/Oregon - (58-50 Ma) - tholeiitic basalts turn to alkalic or calc-alkaline basalts.

2. Tillamoock Oregon Caldera - (54 to 39 Ma) - calc-alkaline basalts turn to silicates.

The older Clarno Formation consists of Eocene non-marine alkaline to calk-alkaline volcanic rocks and intrusions and volcanogenic sedimentary rocks that reputedly range in age from ca. 54 to 39 Ma

3. Wildcat Mt. Caldera - (41-25 Ma) - John Day Formation - first Thundereggs - Madras, Richardson Ranch, Lucky Strike Mine

Robinson and Brem (1981) divided the John Day Formation into a “western”, “southern”, and “eastern” facies (Figure 1). The “western” facies is divided into members designated alphabetically from A to I (Figure 4; Peck, 1964; Robinson and Brem, 1981; Robinson and others, 1990). The “eastern” facies is divided into four members that include from oldest to youngest the Big Basin, Turtle Cove, Kimberly, and Haystack Valley members (Fisher and Rensberger, 1972). The “southern” facies has not been formally divided into members. The base of the John Day Formation is generally defined by the regionally widespread Member A ash-flow tuff that has 40Ar/39Ar ages of 39.72 ± 0.03 Ma near the Painted Hills, 39.22 ± 0.03 Ma near Clarno, and 39.17 ± 0.15 Ma near Ashwood (Bestland and Retallack, 1994a,b; Smith and others, 1998; Retallack and others, 2000). An ash flow defined as Member I near the top of the formation has been dated at 27.7 ± 0.3 Ma (K/Ar) but may be as young as 22 Ma

Mercury from the impact began reaching the surface in the 39 Ma eruptions.
Intermediate to silicic basement rocks and rocks associated with the Wildcat Mountain caldera are characterized by relatively enriched amounts of Al (aluminum) and corresponding relatively depleted contents of K (potassium), Na (sodium), and Fe (iron). These rocks also display characteristically low contents of incompatible high-field-strength elements (HFSE) such as Nb (niobium) and Zr (zirconium), low contents of Y (yttrium), and, generally, lower abundances of the light rare-earth elements (LREE) La (lanthanum) and Ce (cerium)

Oligocene Crooked River caldera
10–13 Ma younger Lower Crooked volcanic field rocks. Mafic rocks preserved within the Lower Crooked volcanic field are Fe- and Ti-rich tholeiites while silicic rocks are characterized by relatively enriched amounts of Y, Zr, Nb, La, and Ce

?. Smith Rock Caldera, Bend Oregon - 29 Ma
The geology of Smith Rocks is volcanic. It is made up of layers of recent basalt flows overlaying older Clarno ash and tuff formations. Approximately 30 million years ago, a large caldera was formed when overlying rock collapsed into an underground lava chamber. This created a huge amount of rock and ash debris that filled the caldera. That material solidified into rock, becoming Smith Rock tuff. Rhyolite flows intruded along faults in the Smith Rock Tuff. [2] A half million years ago, basalt lava flows from nearby volcanoes covered the older tuff.[3][4][5]

More recently, the Crooked River cut its way through the layers of rock to create today's geographic features. Smith Rock itself is a 3,200-foot (980 m)-high ridge (above sea level) with a sheer cliff-face overlooking a bend in the Crooked River (elev. 2600 ft), making the cliffs about 600 feet high.

Tower Mountain Caldera


OREGON/NEVADA
McDermitt Caldera (16-15.1 Ma)

OREGON/NEVADA/IDAHO
Owyhee-Humboldt Caldera (13.8-12 Ma)

NEVADA/IDAHO
Bruneau-Jarbidge Caldera (12.5-11.3 Ma) Bruneau Thundereggs

IDAHO
Twin Falls Caldera (10-8.6 Ma)
Picabo Caldera (10.2 Ma)
Heise Caldera (6.6-4.4 Ma) V

IDAHO/MONTANA/WYOMING
Yellowstone Caldera (2-0.6 Ma)

The LARGEST Spheroids I know of are at Silver Cliff Colorado, near @nrg Scott Solar's new home.

[1dave]

Where to cut depends on what outcome you want.
The biggest face, most slabs, see the internal structure, best patterns, dendritic patterns, . . .

Sometimes you can make good guesses from the outside appearance, but even then you need a supply of thundereggs from the same source to see how they usually formed.

If you are fortunate enough to dig your own TE's a good practice is to use a permanent marker to mark a "T" on top as gravity often determines what happens inside. This does not always help as earth movements may tip the hardened flows any direction during any part of the later fill sequences.

A brief introduction on how thundereggs form:

1. Magmas are modified over time.
Mantle material is heavy, mostly iron and magnesium. As continents move over ocean floors (subduction), lightweight surface minerals are forced down and melted, cooling and contaminating the magma. Heavy minerals crystallize and drop out to the bottom of the magma chamber. As the magma makes it's way to the surface it melts the light minerals around it, adding to the contaminants, usually a lot of silicon. First lavas are olivine, next basalt, then andesite, granite, and finally rhyolite and obsidian. These last two are where thundereggs are formed.

2. Highly silicious magmas (around 65- 80%) with a 1-3% water content, begin crystallizing as spheroids.
Above 1100 degrees C, silica crystallizes as crystobalite fibers. Highly silicious magmas are very thick and viscous, but water content makes it fluid and runny, like adding ball bearings to layers. This allows glide planes to slip and slide, allowing silicon molecules to come into contact with other molecules that normally could not happen. They form like dandelion puffballs.
Geologists call this "spheroidal structure."


Spheroid Formation

Cristobalite needles begin radiating out from a seed molecule, forcing impurities away, and then the "endothermic exothermic dance" begins. The friction of crystallization generates heat! So much so that it becomes too hot for cristobalite to crystallize, but just right for feldspar (the constituents of which have just been enriched) to resume, so a layer of feldspar encapsulates the needles. The magma cools down and cristobalite resumes with another layer of needles. Layer after layer is deposited as the spheroids grow larger and larger - up to ten or twelve feet in diameter!

"Siamese" spheroids in obsidian that almost became thundereggs, from @rockpowell .

3. As the magma finally cools and contracts, internal pressure drops slowly, allowing the trapped water to finally expand into steam, up to 2,000 times it's original dimensions. If the flow is still moving the spheroids can be stretched out into torpedo shapes. If close to the surface, as pressure decreases they can blow to pieces like a bomb.
The deeper in the flow they were, (also, the less the water content) the less they were able to open.
Geologists call this "lithophasal structure."

From the Geode Kid, Richard Paul Colburn.

How they opened also depended on where the water concentrated. In some flows it was in the upper part of the spheroid and there is where the expansion took place.
The Spencer Idaho precious opal thundereggs were the reverse, most of them pushed the old center up with the cavity below.

Occasionally the water collected in many layers, and forced many of them apart.

Image courtesy of the Geode Kid.



Mexican "Coconuts" usually split right to the center (because of so much calcium?) but usually the center sphere remains attached to the largest plate.

Exterior "suture lines" from where it fractured can assist in showing what to expect inside. Just a split between top and bottom will be a "bi-conoid," like two Chinese coolie hats. The sides may have two or three side sutures. Most have four, giving a "box core" shaped interior. If five side sutures are present, cutting through them will reveal a five point star.

4. Over time some cavities are filled with varying temperature ground waters that deposited their mineral loads. You can tell by the weight if the TE is solid, half full, or empty.
Location, location, location! What minerals are in the ground where the thundereggs formed? Just silica? expect clear agate and crystals.
Iron? expect reds and yellows, and possibly amethyst crystals. lots of metals? perhaps you have hit the jackpot as was the case with the Priday plume TE's, with plumes, moss, dendrites, lace patterns. Colors depend on which metals were present.
What was the temperature during fill? If high enough to overcome gravity, expect "fortification" patterns as crystallization took place from all the walls to the center. Cooler liquids placed their deposits from the floor up, flat layer after layer of "waterline agate and opal."

Sometimes TE exteriors are coated with small spheroids, making orientation difficult, but Knowledge of the structure of most TE's will provide the best guess as to where to cut.





With Spencer opal, you need to cut out the flat fire lines. With waterline agate this may also reveal dendrite layers.

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Thunderegg cores

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Figure 5.10, Drawings 1, 2 and 3: Cutting Orientation and Marking In-situ.
From: The Formation of Thundereggs-Revised 2004 by the Geode Kid.

Drawing 1 is the correct cutting orientation for thundereggs with geometric pressure ridges such as those found at the Priday Ranch deposits like the one shown in Figure 5.08. The tops and bottoms are obvious on these types because there are two ridges, one encircling the upper, the other, the lower circumference of each. They can be imagined as the two tropical latitudes drawn on a globe of the Earth.
There are usually four, sometimes five, vertical ridges intersecting with, but not continuing past the two longitudinal ridges. When correctly cut, all the possible sequences of fills will be in chronological order.



Drawing 2 on the next page below shows the correct cutting orientation for thundereggs showing flow bands. Flow banding is an expression of flowage of the lava they were in which, of course, is horizontal over the surface it flowed. These types often show a slightly to exaggerated drawn out ovoid appearance which is also horizontal with the flow bands so, in most cases, cut perpendicular to them and through the long axis.



If , however, a deposit has been deformed before any type of nodules have been filled, the external features become useless so thundereggs must be marked in-situ, i.e., before removing them as instructed in Drawing 3, also below.

[1dave]

[1dave]

Dec 28, 2020 23:19:38 GMT -7 @stephan said:

Great series. Thanks, 1dave

I just edited the first post and will have to make more corrections. With new information about silica gels I'm forced to re-think -

Agate deposited by high temperature water grows from the outside walls to the center

- "Fortification Agate."

Agate deposited by cool water forms flat layers on the floor of voids

-"Water Line Agate."

I'm now thinking quantity of gel water rather than temperature is the controlling factor between waterline and fortification.

Dec 29, 2020 8:48:50 GMT -7 @stephan said:

Dec 29, 2020 8:46:14 GMT -7 1dave said:

I just edited the first post and will have to make more corrections. With new information about silica gels I'm forced to re-think -

I'm now thinking quantity of gel water rather than temperature is the controlling factor between waterline and fortification.

So basically the viscosity?

Yes. At room temperatures the gel is evolving into needles, spheres, various submicroscopic crystals.

Hollows in rocks - whether they be amygdaloids, lithophysae, or any other void below the water table is at some time filled with water.
With earthquakes much of the water is converted to silicic acid that enters the voids.



If the void is filled the dimers, trimers, etc. begin attaching to ALL the walls.

If only a small amount enters, they can only attach at the floor.

IF the next fluid is of high pH some of the material is dissolved and re-deposited as the pH lowers.

There are four varieties of Geodes, Five if you count somewhat similar VUGS.

1. Sedimentary voids from some mineral being dissolved, the void later being filled with agate and crystals. Nearby hot springs present or past is a factor. Without them you have just dead rocks. The hillside where the spring was will be littered with agate nodules, the surrounding area, nothing.
They may turn up in unexpected locations, and usually have an irregular shaped exterior.



2. a "MUST SEE" at: Sedimentary Geodes from a Mississippian extinction event. They are usually fairly spherical, found in Mississippian age mud and waterway bottom soils from Montana to Georgia.
My best guess is a volcanic eruption melted huge amounts of limestone releasing vast heavy clouds of CO² gas that displaced oxygen in the sea. The creatures and their scavengers died, the bodies bloated, then agate and amazing crystals filled the cavities.



3. Igneous Bubble Geodes scientifically known as "Amygdaloids" because some are almond or teardrop shaped. They are formed in fluid basalt and andesite flows that overrun some bedrock that releases gas on heating.
Download Screen Optimized (7Mb) PDF:
Milford Map
ngmdb.usgs.gov/Prodesc/proddesc_9991.htm





Some geodes have a smooth exterior, but often they were surrounded with a frothy foam that gave them a hammered looking exterior.



Amazing are the "Cathedral Geodes" from Brazil that may rise to 7-8 feet tall. Notice how the bottoms were sucked up as the gas cooled.

The bubbles usually remained empty for millions of years until mineral laden fluids began percolating through them. Fill tubes where the materials entered and exited are usually visible.

Andesite has a courser crystal structure than basalt, so bubbles in it are much more irregular, but with a more varied selection of mineral salts, often has far more dramatic fill sequences!


Andesite

In a category all by themselves are the chalcedony worm exteriors of Ocos from from Três Pinheiros, Fountoura Xavier, Rio Grande do Sul, Brazil.


Ocos

4. Thundereggs scientifically known as "Lithophasae." Look on geology maps for that word or Spheroids.
Geologic map and sections of the area between Hamlin Valley and Escalante Desert, Iron County, Utah


Just find the pink "Tsr" locations on the map and check them out!



They 0occur only in high silica content obsidian, pitchstone, rhyolite flows, and Welded Ash Flow Tuffs. But not just any old flow. The pressure and water content had to be just right. About 1-3%. High silica flows are very viscus. They tend to dome up rather than flow. Add a little water and it is like adding marbles. Glide planes come into being where the water is, allowing dry layers to slip along on them.
That allows silica molecules to come in contact with each other that normally would be impossible. Even down in the magma chamber and vent throat, silica needles gather together like dandelion puffballs - Spheroids.

Strike up the band. The "Endothermic/Exothermic Dance" is in full swing.

Crystallization generates heat. If the minerals are present to form feldspar, that activity resumes and cristobalite ceases. A layer of perthite feldspar coats the spheroids. Cooling resumes and so does another layer of cristobalite needles as the spheroids get larger. The cycles may continue for thousands or millions of times. Finally the flow cools enough for the matrix to contract and allow the trapped water to flash into steam, forcing the spheroids to blossom into Thundereggs.

A "Siamese" spheroid "just barely thunderegg" in obsidian.



When you get into an area with lots of little spheroids and "snowflakes" you are in thunderegg country. This is from the Baker egg Mine in New Mexico.



When not coated with tiny eggs, you can see the suture lines where the spheroids were forced apart by steam.



The largest plate will still be attached to the center. a judicious cut can reveal how it expanded.



"Mexican Coconuts" formed the same way, but in carbonate melts that open to the very center. They have lots of calcite crystals throughout the shells and sometimes inside.


Mexican Coconut with Calcite plates


5. Vugs are formed in Pegmatites, granite masses that have been re-injected and enriched from time to time with new surges of gas and magma. This produces pockets known as vugs where large crystals can form. If you find the word Pegmatite on a geologic map in your area, it is definitely worth your time exploring. Topaz, tourmaline, all kinds of beryls . . . the good stuff!

Happy Hunting!

[1dave]

Agate is sedimentary in nature but often forms in various volcanic rocks. As these rocks are often metal rich, this can produce desirable colors and patterns.

BASICS:
1. The SiO² content of Magmas tend to increase over time as they age and high temperature minerals crystallize and drop out.

Olivine > 35% SiO², Basalt > 45% SiO², Andesite > 55% SiO², Rhyolite > 65% SiO²

2. SiO² is easily dissolved by high PH hot water and precipitated in voids by low PH water.

The more SiO² in an area, the more likely Agate is to form.

Agate deposited by high temperature water grows from the outside walls to the center

- "Fortification Agate."

Agate deposited by cool water forms flat layers on the floor of voids

-"Water Line Agate."

1. Gas Bubbles in Basalt and Andesite, commonly fill with agate and are known as Geodes (earth shaped). A careful search may reveal the paths where fluid entered and exited.

Formed in Basalt


Formed in Andesite.

2. Spheroids in Rhyolite and Obsidian can fill with agate and are commonly known as Thundereggs.

Priday Plume - Richardson Ranch, Madras Oregon.

3. Rhyolite Clinkers can be surrounded by agate forming spectacular patterns.

Lavic

4. Highly siliceous Ash Flow Tuff racing along at 300-400 mph can produce amazing Moss, Plume, and Flame patterns.


5. Metamorphic volcanic rocks such as rhyolite can also provide desirable colors and pasterns.

Indian Blanket - posted by @beefjello

[1dave]

1. Gas Bubbles (Amygdaloids) in Basalt and Andesite

Billions of years ago earth's basalt reached the surface at 3,000^oC.
Today it is seldom above 1,200⁰C, but is still very fluid and can flow for hundreds of miles before cooling.
When a flow covers moist ground, the water turns to steam and fills the basalt with gas bubbles.

As the basalt cools and contracts, billions of fractures are created, allowing rainwater to dissolve alkalies and silica that fill the voids. changes in minerals and temperature determine whether the voids are filled with chalcedony, moganite, twisting agate fibers ignoring gravity until lower temperatures allow gravity to take over and produce flat layers.

Basalt generally has a composition of 45–55 wt% SiO2, 2–6 wt% total alkalis, 0.5–2.0 wt% TiO2, 5–14 wt% FeO and 14 wt% or more Al2O3. Contents of CaO are commonly near 10 wt%, those of MgO commonly in the range 5 to 12 wt%.

Over time the voids fill with mineralised water that depending on temperature and ph collect on sides and at cooler temperatures in planes on the bottom.

Sometimes a new eruption will re-heat the fluids and Fortification agate will form again on top of the waterline agate.






Brazilian geodes still in the matrix.

Basalt tends to be fine grained, so gas bubbles in it have fairly smooth surfaces.

As the heavy minerals drop out of solution more feldspar and other lightweight crystals form so bubbles in Andesite have more rugged surfaces.

[1dave]

2. Spheroids (Lithophasae) in Rhyolite and Obsidian

The mineral content of magma is constantly changing as iron and magnesium combine to form olivine crystals; calcium, sodium, and potassium form feldspars and they drop out of solution, making it more and more silica laden over time.

Basalt ~ 45% Silica, Andesite ~ 55% Silica, Rhyolite ~ 65% Silica

BUT the Thunderegg Shells reach over 70% Silica!

- - - - - - - - - - - - - - - - - - - -

At 1,100^oC crystobalite needles form, making "puffballs" with very hot water trapped between the needles. The needles push out the calcium, sodium, and potassium molecules. All that movement causes friction and makes the magma hotter. It becomes too hot for crystobalite to form, but just right for Perthite feldspar to form a sphere around the puffball. The magma cools and crystobalite needles resume.

You see them all the time as "Snowflake Obsidian."

A Thunderegg Siamese Twin that formed in obsidian.


As the flow slowly cools and contracts, pressure is released and the water is finally allowed to expand into steam, forcing the needles apart.


As the gas forces the matrix apart around the thunderegg, "sutures" are formed where the sections break apart.
If the gas escapes the sutures are sucked in.

Later the Spheroid voids are filled with agate the same way as they are in basalt voids.


Finally the temperature becomes so cool crystobalite needles can no longer exist and they revert to other SiO2 forms, but they sometimes leave imprints to prove they once existed.

Thunderegg Cores - the outer shells removed.

[1dave]

3. Rhyolite Clinkers

Rhyolite is so thick as a liquid that instead of flowing, it often domes up as it did in Mt. St. Helen.





But sometimes repeated eruptions flow and form layers.



outsidetheinterzone.blogspot.com/2014/03/geo-730-march-12-day-436-lithophysal.html

Rhyolite is a high-silica lava, typically 70% (plus or minus a little) SiO2 by mass. In molten form the silica tends to stick together in chains, like a polymer, so it's "sticky." It tends to be quite viscous, or resistant to flow, and ions have a difficult time migrating into stable crystal nucleation and growth sites. Thus, when they cool fairly quickly- and especially if they have low water content (Water acts in an opposite manner to silica: it makes molten rock less viscous and increases ion mobility)- lavas like rhyolite tend to be glassy. And as I mentioned yesterday, this outcrop is quite glassy.

I was warned by Sharky on my first visit to this spot that "They're glassy, so be careful." Being the bright student I was (and dressed in a tee-shirt and shorts, but thankfully, also thick glasses), I walked up to a solid exposure and gave it a sharp thwack with my hammer. Then spent several minutes picking out splinters of glass from my arms, legs and face. Ah, the joys of field geology...

As lava flows, the top tends to move forward while the bottom sticks to the ground. This is known as "Caterpillar Action."



"Clinkers" are lava fragments formed by fragmentation of a cooling crust because of an increase in viscosity and in shear strain rate.
Surface clinkers are transported to the flow front by caterpillar motion, piled at the flow base, then buried as the flow covers them.

Clinkers are fragmented in three different ways.

1. Surface Clinkers can form by cooling contraction and eventually become roll-over basal breccia by caterpillar action.

2. Internal Clinkers can form from brittle brecciation by internal and basal shear forces.

3. Basal Clinkers can form from Water/lava interactions. Water/lava ratio variations may produce different clinker structures, in a manner similar to observed textural changes in phreatomagmatic eruptions. A transition from clinkery particles to angular blocky particles is interpreted as an increase in groundwater inflow.

When those spaces are filled with agate, it is time for the RTH Rock Rescue Teams to be called in!



rockgemmineralclubs.blogspot.com/2010/05/afms-field-trip-lavic-siding.html

[1dave]

4. Highly Siliceous Ash Flow Tuff

Material expelled in volcanic eruptions can be classified as:

1. Volcanic gases, a mixture made mostly of steam, carbon dioxide, and a sulfur compound - either sulfur dioxide, SO2, or hydrogen sulfide, H2S, depending on the temperature.
2. Lava, the name of magma when it emerges and flows over the surface.
3. Tephra, (Tuff) chunks of solid material of all shapes and sizes ejected and thrown through the air. Chunks smaller than 2 mm in diameter (sand-sized or smaller) are called volcanic ash.

Adding water to Rhyolite filled volcanoes can become explosive!



Here we are covering THREE separate subjects:
1. Ash FALL flat layers
2. Ash FLOW sloped layers
3. Welded Ash Flow layers



As ash fall flat layers rate -10 on a blah scale from 1 down to -10, - - -

let's look at Ash FLOW sloped layers. They are Volcanic Land Slide Debris that traveled at various degrees of hotnesss, gassiness, and wetness.

They consist of whatever was accumulated on the side of the volcano from all previous eruptions.
There are 6 Types depending on depth and age of magmas and what has collected on volcanic hillsides: 1. Welded tuff, 2. Rhyolitic tuff, 3. Trachyte tuff, 4. Andesitic tuff, 5. Basaltic tuff, 6. Ultramafic tuff

Lava, pumice, basalt, andesite, obsidian, rhyolite, agate, wind blown sand that suddenly moved away from a volcano at 100 km/h (62 mph) on average but is capable of reaching speeds up to 700 km/h (430 mph).[2] The gases can reach temperatures of about 1,000 °C (1,830 °F).

The word pyroclast is derived from the Greek πῦρ, meaning "fire", and κλαστός, meaning "broken in pieces".[3] A name for pyroclastic flows which glow red in the dark is nuée ardente (French, "burning cloud"); this was first used to describe the disastrous 1902 eruption of Mount Pelée on Martinique where over 30,000 people were killed.

Ash Flow Tuff may be fine or course grained mixtures sometimes resembling conglomerates.



But, as at Holt Canyon in southwestern Utah, they can be far more interesting.

Ash FLOW slopes can appear in an instant over a large area, and hundreds of feet thick.

Then something interesting begins to happen inside of them.

Hot gas is expelled from the surface, glass shards begin to de vitrify, heat builds up in the core, pressure collapses space between shards, and glass shards begin to weld together.
This is reversed at the base where the cool ground underneath stops the process.











en.wikipedia.org/wiki/Pyroclastic_flow

A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud)[1] is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that moves away from a volcano about 100 km/h (62 mph) on average but is capable of reaching speeds up to 700 km/h (430 mph).[2] The gases can reach temperatures of about 1,000 °C (1,830 °F).

Pyroclastic flows are a common and devastating result of certain explosive eruptions; they normally touch the ground and hurtle downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope.

The word pyroclast is derived from the Greek πῦρ, meaning "fire", and κλαστός, meaning "broken in pieces".[3] A name for pyroclastic flows which glow red in the dark is nuée ardente (French, "burning cloud"); this was first used to describe the disastrous 1902 eruption of Mount Pelée on Martinique.[4][note 1]

Pyroclastic flows that contain a much higher proportion of gas to rock are known as "fully dilute pyroclastic density currents" or pyroclastic surges. The lower density sometimes allows them to flow over higher topographic features or water such as ridges, hills, rivers and seas. They may also contain steam, water and rock at less than 250 °C (482 °F); these are called "cold" compared with other flows, although the temperature is still lethally high. Cold pyroclastic surges can occur when the eruption is from a vent under a shallow lake or the sea. Fronts of some pyroclastic density currents are fully dilute; for example, during the eruption of Mount Pelée in 1902, a fully dilute current overwhelmed the city of Saint-Pierre and killed nearly 30,000 people.[5]

en.wikipedia.org/wiki/Tuff

Tuff (from the Italian tufo), also known as volcanic tuff, is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation. Tuff is sometimes[when?] erroneously called[by whom?]"tufa", particularly when used as construction material, but properly speaking, tufa is a limestone precipitated from groundwater. Rock that contains greater than 50% tuff is considered tuffaceous.

Tuff is a relatively soft rock, so it has been used for construction since ancient times. Since it is common in Italy, the Romans used it often for construction. The Rapa Nui people used it to make most of the moai statues in Easter Island.

Tuff can be classified as either sedimentary or igneous rock. They are usually studied in the context of igneous petrology, although they are sometimes described using sedimentological terms.

There are 6 Types depending on depth and age: 1. Welded tuff, 2. Rhyolitic tuff, 3. Trachyte tuff, 4. Andesitic tuff, 5. Basaltic tuff, 6. Ultramafic tuff

Rhyolitic tuff
Light-microscope image of tuff as seen in thin section (long dimension is several mm): The curved shapes of altered glass shards (ash fragments) are well preserved, although the glass is partly altered. The shapes were formed about bubbles of expanding, water-rich gas.
The rhyolitic tuff portal of the "church house" at Colditz Castle, Saxony, designed by Andreas Walther II (1584)

For petrographical purposes, tuff is generally classified according to the nature of the volcanic rock of which it consists; this may be the same as the accompanying lavas if any were emitted during an eruption, and if a change occurs in the kind of lava which is poured out, the tuffs also indicate this equally clearly. Rhyolite tuffs contain pumiceous, glassy fragments and small scoriae with quartz, alkali feldspar, biotite, etc. Iceland, Lipari, Hungary, the Basin and Range of the American southwest, and New Zealand are among the areas where such tuffs are prominent. The broken pumice is clear and isotropic, and very small particles commonly have crescentic, sickle-shaped, or biconcave outlines, showing that they are produced by the shattering of a vesicular glass,[1] sometimes described as ash-structure. The tiny glass fragments derived from broken pumice are called shards; the glass shards readily deform and flow when the deposits are sufficiently hot, as shown in the accompanying image of welded tuff.

In the ancient rocks of Wales, Charnwood, the Pentland Hills, etc., similar tuffs are known, but in all cases, they are greatly changed by silicification (which has filled them with opal, chalcedony, and quartz) and by devitrification. The frequent presence of rounded corroded quartz crystals, such as occur in rhyolitic lavas, helps to demonstrate their real nature.[1]

An example of this tuff, Rochlitz Porphyr, can be seen in the Mannerist-style sculpted portal outside the chapel entrance in Colditz Castle.[2] The trade name Rochlitz Porphyr is the traditional designation for a dimension stone of Saxony with an architectural history over 1,000 years in Germany. The quarries are located near Rochlitz.[3]

[1dave]

Nov 9, 2018 19:08:49 GMT -7 @rwa3006 said:

Interesting! I have a pal, an old timer who has a number of the thunder egg cores like the center one in the bottom most photo of #2. He got them from Dugway and as we were looking them over we noticed that each one has a male and female dimple on opposite sides. You can see the male dimple on the top of yours in your photo. My bud theorizes that the opposite dimples are a result from polarity forces during formation. I have no clue. What do you think?

The "dimple and pimple" is formed at the layer where the most water flashed into steam and pushed the egg open. Sometimes it is on a small sphere layer, sometimes large, and once in a while many layers opened at the same time.

[1dave]

I've become a forgetful old man! This is another thread I started and never got back to.

There is so much to learn!

I'm tempted to start a new thread " The Yin and Yang of SiO² "

Down near absolute ZERO all is quiet on the western front.
Silica and oxygen bonds are at their shortest lengths. all the groups are similar shaped tetrahedrons that stack together in regular fashion to make identical crystals.



As temperatures increase, just like molting creatures changing their exoskeletons, suddenly all the oxygen atoms get bigger ad their bonds jump to a new length! The crystals have to change shapes, just like a brick wall when you change the brick shapes.

Later, the bigger and heavier silicon atoms follow suit, and again, the crystal shapes must change!

Shapes change from a to b, then c, d, e, f ,g, h, but then begin repeating themselves again, only in a larger size as A, B, C, D, E, . . .

For 50 years I studied the high temperature forms of quartz a and b, tridymite a and b, cristobalite a and b.

Now I am realizing those same shapes occurred at and below room temperature as silicic acid polymorphs as monomers, dimers, trimers, etc.!

[1dave]

Nov 13, 2013 11:13:48 GMT -7 @bhiatt said:

Nov 10, 2013 16:33:32 GMT -7 @jawboney said:

Nice egg, what is the matrix that surrounds the agate made of? Odd I don't know because it's something I really should know

dont know the technical term but I think Richardson Ranch t eggs are mud balls.

The thundereggs formed in rhyolite.
The matrix once was white cristobalite needles with various feldspar impurities between them, but that texture is only stable at high temperatures. On further cooling they both re-crystallized as other polymers.





nteresting historical book!

First chapter - spheroid development.
Second chapter - tremendous internal expansion!!!!!!! Spheroid converts to thunderegg.
Third chapter - chamber filled with what appears to be zeolites.
Fourth chapter - zeolites forced to the bottom as dark blue silica laden fluids enter and coat all walls.
As chalcedony crystallization continues, color lightens considerably, then alternately darkens and lightens - "rhythmic crystallization."
Fifth chapter - temperature lowers and final planar agate is formed.

Outstanding!

[1dave]

Jul 15, 2020 11:15:36 GMT -7 @woodman said:

The new bed at the RANCH, are different, the ones I have cut so far are all cresecent shaped. or near to it, they are different for sure.

[1dave]

Aug 3, 2014 10:43:24 GMT -7 @kradz89 said:

Who says  Rockhound is picked over! With the summer rains down here in the Southwest, my husband and I decided to head out to Rockhound. Nice cloudy day in the low 80's due to the rains made for a nice break from our 100 degree weather! So it was slow going at first, then we found THE wash of all washes and jackpot. Thundereggs all over. These are the ones I cut open today, we have more that are already broken open and need to be cleaned up out in the garage still. It is cloudy again today, so not the greatest pictures.

Group shot.
003 by kradzyniak89, on Flickr

Hubby wanted this piece slabbed
004 by kradzyniak89, on Flickr

Close up of one of the slabs
005 by kradzyniak89, on Flickr

Stormy seas!
006 by kradzyniak89, on Flickr

Angel
007 by kradzyniak89, on Flickr

Backside of angel, lucked out on this cut to get the angel!
012 by kradzyniak89, on Flickr

Some jasper included in this spiral.
008 by kradzyniak89, on Flickr


010 by kradzyniak89, on Flickr

011 by kradzyniak89, on Flickr

013 by kradzyniak89, on Flickr

Aug 3, 2014 21:05:58 GMT -7 @quartz said:

Nice finds, I've never seen the ones that are all swirly before. Looks like they filled while rolling down a hill.

They definitely had a tough life! A few cuts show the original spheroid centers.
Some theorize the spheroids began forming while in the magma chamber and continued while being forced up the neck. Pressure would be reduced on reaching the surface, allowing water to flash into steam and expanding them into thundereggs.

Rockhound state park is quite steep. I'm sure lots of tumbling took place.

[1dave]

WeldedAshFlowTuff

reader.elsevier.com/reader/sd/pii/S1876380412600305?token=0488C4D6766A07C749ED51221DEE43EB52FA4DCB0CA91A0CE919127991BEE45A485EF59D73C2BEAC7EF6850EA789D62A

2 Genesis and petrologic characteristics of welded tuffs

2.1 Genesis of welded tuffs
The welded tuffs in the Fengcheng Formation of the study area is made up of ash flows. Because of the abrupt pressure drop and gas expansion during ascension, large quantities of foaming occurs, similar to boiling when acid and intermediate magma with higher viscosity and abundant volatile constituents ascend towards the shallower depths near the surface.

Bubble walls become thinner and thinner, and crack. Finally, the ash erupts from the crater as an intensive explosion. Because of the explosion, the lava column is broken into debris such as vitric debris, crystal debris and volcanic dust. Some of the materials are then thrown into the air, but most are suspended among the volcanic gases in an incandescent state.

Dispersed along the slope at high speed, the debris, like water, finally flows down and fills in low lying areas. After the flow welded tuff. Particles of volcanic ash can be thrown into the
air by explosion and cooled down rapidly, when the volatile constituents escape quickly. Large amounts of heat and volatile constituents are still preserved during the emplacement process of volcanic ash flow tuff, which is favorable for the welding process and the formation of vesicles.

2.1.1 Preservation of heat
The temperature of pyroclastic flows can be up to 715 1 000 C[10]. Because the amount of lost gas during the flowing period is small, large amounts of heat are preserved in the system. The transported heat and heat generated by physical reactions are sufficient to weld the tuffaceous matter. Thick volcanic ash flow tuffs have relatively good thermal insulation properties which can hold the weld temperature for a relatively long period. Because the heat conductivity of porous,glassy pyroclastic rocks containing abundant volatile constituents is poor, it too is more able to preserve the heat [9].

2.1.2 Role of volatile constituents
Volatile constituents can reduce the welding temperature and viscosity of magma, which can in turn promote both devitrification and the formation of vapor phase minerals in open pores [9]. Meanwhile, the existence of gases, such as volatile constituents, is incorporated when pyroclastic flow is surrounded by explosion gas, generating a boiling liquid suspension.

Density is then decreased and the self–exploding is continuous. Pyroclastic flow can flow towards volcanic low lying areas at high speed, leading to a relatively slow loss of heat during pyroclastic flow. Because these relatively high temperatures are retained after emplacement, the pyroclastic flow can become welded [11].