talc

Mg ₆ [Si ₈ O ₂₀ ](OH) ₄ . Also called talc. A phyllosilicate. It has a three-layer structure with a brucite layer {Mg(OH) ₂ } sandwiched between SiO ₄ tetrahedral layers. It occurs naturally as a product of hydrothermal alteration of ultramafic rocks and low-temperature metamorphism of siliceous dolomite. It has a monoclinic crystal system, space group C 2/ c , lattice parameters a ₀ = 0.528, b ₀ = 0.915, c ₀ = 1.89 nm. β = 100°15′. Massive, leaf-like, perfectly cleaved {001}. Hardness 1. Brittle. Density 2.58-2.83 g cm ^-3 . n 1.539-1.600. Birefringence approximately 0.05. Negative biaxiality. Optical axis angle 2 V = 0° to 30°. White, pale green, and greasy. It has a low expansion coefficient and is used as a ceramic raw material, as well as a filler for paints, and as a thermal and electrical insulator. It is not affected by acids.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

Mg₆[Si₈O₂₀](OH)₄．滑石ともいう．フィロケイ酸塩．ブルーサイト層{Mg(OH)₂}をSiO₄の四面体層ではさんだ三層構造をなす．天然には超塩基性岩の熱水変質，ケイ酸質ドロマイトの低温変成の生成物として産出する．単斜晶系，空間群 C 2/c，格子定数 a₀ ＝ 0.528，b₀ ＝ 0.915，c₀ ＝ 1.89 nm．β ＝ 100°15′．塊状，葉片状，へき開{001}完全．硬度1．もろい．密度2.58～2.83 g cm^－3．n1.539～1.600．複屈折率約0.05．二軸性負．光軸角2V ＝ 0°～30°．白色，淡緑色，脂感がある．膨張率が小さいため窯業原料として，その他，塗料用の充填剤，熱，電気の絶縁体として用いられる．酸に侵されない．

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