Also tal·cum[tal-kuh m]/ˈtæl kəm/. a green-to-gray, soft mineral, hydrous magnesium silicate, Mg3(Si4O10)(OH)2, unctuous to the touch, and occurring usually in foliated or compact masses, used in making lubricants, talcum powder, electrical insulation, etc.
a white, grey, brown, or pale green mineral, found in metamorphic rocks. It is used in the manufacture of talcum powder and electrical insulators. Composition: hydrated magnesium silicate. Formula: Mg 3 Si 4 O 10 (OH) 2 . Crystal structure: monoclinic
1550s, from Medieval Latin talcum, used for any of various shiny minerals. See talc.
1580s, from Middle French talc, probably from Spanish talco and Medieval Latin talcum "talc" (ealy 14c.), both from Arabic talq, from Persian talk "talc." "It was applied by the Arab and medieval writers to various transparent, translucent and shining minerals such as talc proper, mica, selenite, etc." [Flood].
A very soft white, greenish, or gray monoclinic mineral usually occurring as massive micalike flakes in igneous or metamorphic rocks. It has a soapy texture and is used in face powder and talcum powder, for coating paper, and as a filler in paints and plastics. Chemical formula: Mg3Si4O10(OH)2.