Talc. Credit: Mineral Information Institute.
Talc is an extremely soft (hardness 1 on the Mohs scale), white or greenish-white mineral composed essentially of magnesium silicate, Mg3Si4O10(OH)2. Talc crystallizes in the triclinic system. It forms as a secondary mineral in metamorphic rocks by alteration of magnesium-rich olivines, pyroxenes, and amphiboles of ultrabasic rocks. It has a soft, soapy texture and a layer structure similar to that of mica. It is used in talcum and face powder, as a paper coating, and as a filler for paint and plastics. Massive fine-grained (compacted) talc is known as soapstone or steatite. Relative density: 2.6.