The Tale of Talc

摘要

Talc is well-known to mineral collectors for its hardness or, more precisely, its lack of hardness. Ranking 1.0 on the Mohs hardness scale, talc is the softest of the more than 5,400 recognized minerals. Talc, or basic magnesium silicate, chemical formula Mg3Si4O10(OH)2, crystallizes in the monoclinic system; usually as foliated or compact masses and only occasionally as tabular crystals. Translucent to opaque and exhibiting perfect one-directional cleavage, talc has a pearly luster, a greasy feel, and colors ranging from white to pale shades of green, yellow, brown, and gray. With a specific gravity of 2.75, it is slightly denser than quartz.