talc - soft white talc from the Acme Mine, Alexander Hills, San Bernardino County, California Unit of 5 student specimens

The Western Talc Mine - Acme mine was the second largest talc mining operation in the Death Valley region. The southern Death Valley area talc deposits are some of the best examples in the U.S. of talc formed by contact metamorphism. Mining began there around 1910. There are at least 43 talc mines and prospects in the region. Only one mine is currently in production. Mines in the Death Valley National Monument ceased production in 1988. This talc formed when a cherty dolomitic horizon at the bottom of the Crystal Spring Formation was intruded by gabbroic sills in the Mesoproterozoic, roughly one billion years ago. The sills were emplaced before the overlying limey sediments had consolidated and while they were saturated, perhaps by marine water from an overlying sea. Contact metamorphism produced the talc along the boundary between the sill and the carbonate metasediments. Two gabbroic sills in the area gave U-Pb radiometric ages of 1087+  and 1069+3 million years. Talc is the softest