Where it forms, where it's found
- Type locality
- Millbury
- Worcester County
- Massachusetts
- USA
42.1939°, -71.7606°
612recorded occurrences
Physical
Optical
- Optical type
- Biaxial (-) · 2V measured = 8°
- Refractive index
- 1.525 – 1.581
- Surface relief
- Moderate
- Principal indices
- nα 1.525 – 1.561 · nβ 1.545 – 1.581 · nγ 1.545 – 1.581
- Dispersion
- weak
Δ = 0Δmax
PPLpleochroism per grain
XPLindependent extinctions · rotate the stage
PPLpleochroism only · colour blends on rotation
XPLinterference colour · extinct every 90°
Retardation200 nm
Order1st order
XPL colour
Crystallography
- Cell parameters
- a = 5.24 Å · b = 9.17 Å · c = 28.6 Å
- Cell angles
- β = 94.6 °
- Ratio a:b:c
- 1 : 1.750 : 5.458
- Z
- 4
- Comment
Space group C2/m (a = 5.24(2), b = 9.17(2), c = 28.60(5) Å, beta = 94°36'(24')°, Z = 4, or space group C2/c (a = 5.349(6), b = 9.255(10), c = 28.89(2) Å, beta = 97°7'(6')°, Z = 4.
Crystal structure
Chemical composition
- Impurities
- Ca
- Na
- K
Synonyms
- Brodrickite
- Culsageeite
- Jefferisite
- Kerrite
- Zonolite
In other languages
- French
- vermiculite
- German
- Vermiculit · Vermiculite · Wurmstein
- Spanish
- vermiculita
- Italian
- vermiculite
- Portuguese
- vermiculita · Vermiculite
- Japanese
- バーミキュライト · ヒル石 · 膨張ひる石 · 蛭石
- Chinese
- 蛭石
- Simplified Chinese
- 蛭石
- Traditional Chinese
- 蛭石
- Russian
- вермикулит
- Arabic
- الفيرميكيوليت · فيرميكوليت
Classification
Strunz
10th ed.9.EC.50
- 9SilicatesClass
- 9.EPhyllosilicatesDivision
- 9.ECPhyllosilicates with mica sheets, composed of tetrahedral and octahedral netsGroup
- 9.EC.50VermiculiteSpecies
Dana
8th ed.71.02.2d.03
- 71Phyllosilicates Sheets of Six-membered RingsClass
- 71.02Sheets of 6-membered rings with 2:1 layersType
- 71.02.2d— unnamed intermediate level —Group
- 71.02.2d.03VermiculiteSpecies
CIM
—16.19.22
- 16Silicates Containing Aluminum and other MetalsClass
- 16.19Aluminosilicates of Fe and MgGroup
- 16.19.22VermiculiteSpecies
Group, growth & confusion
Literature, links & citation
Citations
- 1824Webb, T.H. (1824): New localities of tourmalines and talc. American Journal of Science and Arts, 7, 55. ["I term it Vermiculite (worm breeder) from Vermiculor, to breed or produce worms."]
- 1941Ruthruff, Robert F. (1941) Vermiculite and hydrobiotite. American Mineralogist, 26 (8) 478-484
- 1956Weiss, E. J., Rowland, R. A. (1956) Effect of heat on vermiculite and mixed-layered vermiculite-chlorite. American Mineralogist, 41 (11-12) 899-914
- 1966Shirozu, Haruo, Bailey, S. W. (1966) Crystal structure of a two-layer Mg-vermiculite. American Mineralogist, 51 (7) 1124-1143
- 1975Bailey, S. W. (1975) Cation ordering and pseudosymmetry in layer silicates: Presidential Address, 1974. American Mineralogist, 60 (3-4) 175-187
Cite this entry
@misc{mineral2026,
author = {Mineral Index editorial board},
title = {Vermiculite — Mineral Index},
year = {2026},
url = {https://mineralindex.org/minerals/vermiculite-4170},
note = {Accessed 2026-05-11}
}