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.
| Talc. Credit: Mineral Information
AND PLANETARY SCIENCE