Talc

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Talc
Talc.jpg
Crystals o talc
General
Category Silicate mineral
Formula
(repeating unit)
Mg3Si4O10(OH)2
Strunz classification 9.EC.05
Crystal symmetry Either monoclinic 2m or triclinic 1[1]
Unit cell a = 5.291 Å, b = 9.173 Å, c = 5.290 Å; α = 98.68°, β = 119.90°, γ = 90.09°; Z = 2 or
a = 5.287 Å, b = 9.158 Å, c = 18.95 Å, β = 99.3°; Z = 4[1]
Identification
Color Licht tae dark green, broun, white, grey
Crystal habit Foliatit tae fibrous masses, rare as platey tae pyramidal crystals
Crystal seestem monoclinic or triclinic[2]
Cleavage Perfect on {001} basal cleavage
Fractur Flat surfaces (not cleavage), fractur in an uneven pattern
Tenacity Sectile
Mohs scale hairdness 1 (definin mineral)
Luster Waxlike or pearly
Streak White tae pearl black
Diaphaneity Translucent
Specific gravity 2.58 tae 2.83
Optical properties Biaxial (-)
Refractive index nα = 1.538 – 1.550
nβ = 1.589 – 1.594
nγ = 1.589 – 1.600
Birefringence δ = 0.051
Pleochroism Weak in dark varieties
Ultraviolet fluorescence Short UV=orange yellae, lang UV=yellae
References [1][3][4]

Talc (derived frae Persian: تالک tālk; Arabic: تلكtalk) is a mineral componed o hydrated magnesium silicate wi the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2. In loose furm, it is the widely uised substance kent as talcum pouder. It occurs as foliatit tae fibrous masses, an in an exceptionally rare crystal furm. It haes a perfect basal cleavage, an the folia are non-elastic, altho slichtly flexible. It is the saftest kent mineral an leetit as 1 on the Mohs hairdness scale. It can be easily scratched bi a fingernail. It is an aa sectile (can be cut wi a knife). It haes a specific gravity o 2.5–2.8, a clear or dusty luster, an is translucent tae opaque. Talc is nae soluble in watter, but it is slichtly soluble in dilute mineral acids. Its colour ranges frae white tae grey or green an it haes a distinctly greasy feel. Its streak is white.

Soapstone is a metamorphic rock componed predominantly o talc.

References[eedit | eedit soorce]

  1. 1.0 1.1 1.2 Handbook of Mineralogy
  2. An Introduction to the Rock-Forming Minerals, second edition, by W.A. Deer, R.A. Howie, and J. Zussman, 1992, Prentice Hall, ISBN 0-582-30094-0.
  3. Talc at Mindat.org
  4. Talc at Webmineral