talc A member of the 2:1 phyllosilicates (sheet silicates) with composition Mg₆[Si₄O₁₀]₂(OH)₄; sp. gr. 2.58–2.83; hardness 1 (it has the lowest hardness on Mohs's scale of hardness); monoclinic; rare crystals are tabular, often massive; white to green; cleavage perfect hardness; massive talc (soapstone or steatite) can be formed during the low-grade metamorphism of siliceous dolomites; and as a secondary mineral during hydrothermal alteration of ultrabasic igneous rocks along shear planes. It is associated with serpentization with serpentine changing to talc and magnetite by addition of CO₂. It is used extensively as a mineral filler.

talc / talk/ • n. talcum powder. ∎  a white, gray, or pale green soft mineral with a greasy feel, occurring as translucent masses or laminae and consisting of magnesium hydroxyl silicate.• v. (talced, talc·ing) [tr.] powder or treat (something) with talc.DERIVATIVES: talc·ose / ˈtalkōs/ adj. ( Geol. ).talc·y / ˈtalkē/ adj.

talc (hydrous magnesium silicate, Mg₃Si₄O₁₀(OH)₂). It occurs as rare tabulate crystals in a monoclinic system and as masses. It is used as base for talcum powder and in ceramics. Hardness 1; r.d. 2.6.

talc species of translucent or shining minerals, e.g. mica. XVI. — F. talc or medL. talcum (whence talcum XVI) — Arab. ṭalḳ — Pers. talk.

talc (tal'k) n. a soft white powder consisting of magnesium silicate, used as a dusting powder.