Mineral Information and Data:

Vermiculite
Mg0.7(Mg,Fe3+,Al)6(Si,Al)8O20(OH)4 • 8H2O [CNMNC approved formula]

Named from the Latin "vermiculare", to breed worms, in allusion to its peculiar exfoliation on intense heating.

IMA status : Valid species (Pre-IMA 1824) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
71.02.02d.03  
  (71) Phyllosilicate Sheets of Six-Membered Rings
  (71.02) with 2:1 Layers
  (71.02.02d) Mica Group (Hydromica subgroup)
  
Nickel-Strunz
(10th edition) :
09.EC.50
  (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 = 5.24Å, b = 9.17Å, c = 28.6Å β = 94.6°
Crystal Habit: Large plates which may have hexagonal shape
  
Color: Colorless, white, yellow, green, brown
Diaphaneity: Translucent
Luster: Dull to pearly, bronze
Hardness (Mohs): 1.5 to 2
Measured Density: 2.2 to 2.6 g/cm3
Cleavage: 1; {001} perfect
Tenacity: Pliable, when in large replacement sheets
  
Geologic Setting: An alteration product of biotite or phlogopite, by weathering or hydrothermal action. Formed at the contact between felsic and mafic or ultramafic rocks such as pyroxenites and dunites; in carbonatites and metamorphosed limestones; a clayey constituent of soils.
Mineral Association: Corundum, apatite, serpentine, talc; interstratifies with chlorite, biotite
  
Synonyms/varieties: Brodrickite, Culsageeite, Jefferisite, Zonolite
Comments: Vermiculite is mined as a natural insulation material.

 

Vermiculite
Variety jefferisite
Origin: Brinton's Quarry, Chester County, Pennsylvania, U.S.A.
Sample size: 13 x 10 x 1 cm
Photo: Rob Lavinsky

 

Vermiculite
Origin: Kovdor, Kola Peninsula, Russia
Sample size: hand specimen
Photo: Diederik Visser

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