When the Pioneers first entered Beaver county, on the south side of Mineral Mountain they found an egg shaped piece of Lead/Silver metal about 800 feet in diameter, and started Minersville. They used the metal to make shoes for their horses and oxen and bullets - starting the stories of the Lone Ranger. The area was originally limestone.Apparently the original impact was sufficient to shatter the limestone and fill the cracks with Silver Chloride and change the limestone to marble.