Mineral Information and Data:

Talc
Mg3Si4O10(OH)2 [CNMNC approved formula]

Named from the Arabic talq = pure.

IMA status : Valid species (Pre-IMA 1546) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
71.02.01.03  
  (71) Phyllosilicate Sheets of Six-Membered Rings
  (71.02) with 2:1 Layers
  (71.02.01) Pyrophyllite-talc group
  
Nickel-Strunz
(10th edition) :
09.EC.05
  (09) Silicates
  (09.E) Phyllosilicates
  (09.EC) Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 5.29 Å, b = 9.16 Å, c = 18.95 Å, b = 92.5°
Crystal Habit: Crystals thin tabular, to 1 cm, massive, fine grained compact, foliated or fibrous, globular stellate groups
  
Color: Pale green to dark green, greenish gray, white, silvery white
Diaphaneity: Transparent, Translucent
Luster: Pearly or dull
Hardness (Mohs): 1
Measured Density: 2.58 to 2.83 g/cm3
Cleavage: 1; {001} perfect
Tenacity: Sectile; flexible but not elastic
Streak: White
  
Polymorphism and Series: Polytypes: 1A, 2M1.
Geologic Setting: In talc-rich schists or steatite through hydrothermal alteration of mafic rocks (steatitization) subsequent to serpentinization during greenschist facies metamorphism. Also formed by thermal low-temperature metamorphism of siliceous dolostones.
Mineral Association: Actinolite, tremolite, chlorite, pyroxene, vermiculite, serpentine, anthophyllite,
dolomite, calcite
  
Synonyms/varieties: Agalmatolite, kerolite (hydrous variety), soapstone (compact variety), steatite (massive, impure variety)
Other Properties: Gemstone Unlikely Available.

 

Talc
Light-green crystals with calcite
Origin: Rozna, Czech Republic
Sample size: 5 x 5 cm
Photo: Diederik Visser

 

Talc
Origin: Lom, Norway
Sample size:5 x 4.5 x 3 cm
Photo: Tom Loomis

 

Talc
(zoom-in of above)

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