Lepidolite; From 2,640 million year old Tanco rare-element granite pegmatite; Bird River Belt, Manitoba; Donated by Tantalum Mining Corporation of Canada.
The Tanco pegmatite contains a variety of metals, such as lithium, cesium, rubidium, beryllium and tantalum. The Tanco Mine, which exploits this deposit, is the world’s largest producer of cesium. A pegmatite forms when magma, fluid rock deep below the surface, crystallizes slowly, concentrating rarer elements in the remaining solution, which eventually solidifies. The minerals formed from these concentrated solutions are the source of some of the rarer elements associated with this deposit.
Lepidolite is a member of the mica group, which forms in granite pegmatites, and is a source of rubidium and cesium.