Crystals of talc.
Category Silicate mineral
Chemical formula Mg3Si4O10(OH)2
Color white, grey, green, blue, or silver
Crystal habit foliated to fibrous masses
Crystal system Monoclinic or Triclinic[1]
Cleavage perfect basal cleavage
Fracture Flat surfaces (not cleavage) fracture in an uneven pattern
Tenacity Sectile
Mohs scale hardness 1
Luster waxlike or pearly sometimes smooth
Streak White
Diaphaneity Translucent
Specific gravity 2.58 to 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
Other characteristics Fluorescent
References [2][3][4]


  1. 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.
  2. http://rruff.geo.arizona.edu/doclib/hom/talc.pdf Handbook of Mineralogy
  3. http://www.mindat.org/min-3875.html Mindat.org
  4. http://webmineral.com/data/Talc.shtml Webmineral data