Talc is a common metamorphic mineral on the Mohs hardness scale. The hardness of talc is the smallest and equal to one. To the touch, talc is greasy. It is divided into several types. Talc was mentioned in the writings of George Agricolla, a Renaissance scientist.
You can see talc stone for sale and buy it in the Minerals of Russia online store.
General | |
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Category | Silicate mineral |
Formula (repeating unit) |
Mg3Si4O10(OH)2 |
IMA symbol | Tlc |
Strunz classification | 9.EC.05 |
Crystal system | Monoclinic or triclinic |
Crystal class | Either prismatic (2m) or pinacoidal (1) |
Space group | C2/c or C1 |
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 |
Identification | |
Color | Light to dark green, brown, white, grey, colorless |
Crystal habit | Foliated to fibrous masses, rare as platey to pyramidal crystals |
Cleavage | Perfect on {001} basal cleavage |
Fracture | Flat surfaces (not cleavage), fracture in an uneven pattern |
Tenacity | Sectile |
Mohs scale hardness | 1 (defining mineral) |
Luster | Waxlike or pearly |
Streak | White jot to pearl black |
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 |
Ultraviolet fluorescence | Short UV=orange yellow, long UV=yellow |