- The mineral was first described in 1824 by Thomas H. Webb. Due to the property of the mineral to expand into worm-like formations when heated to 200 to 300 °C in the direction of the crystallographic c-axis, Webb named it after the Latin word “vermiculor” for “worm breeder”.
- On the occasion of the 195th anniversary of its discovery and due to its great importance as an industrial mineral, vermiculite was voted “Mineral of the Year” in Austria in 2019.
- Formula: Mg0,7(Mg,Fe,Al)6(Si,Al)8O20(OH)4 · 8 H2O
- Space group: C2/c (No. 15)
- Crystal system: monoclinic
- Crystal class: 2/m
- Lattice parameters: a = 5.349 Å, b = 9.255 Å, c = 28.89, α = γ = 90°, β = 97.12°
Picture: CC BY-SA 3.0 Leon Hupperichs
Crystal structure (click on the picture to download the VESTA file):
(K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,”J. Appl. Crystallogr., 44, 1272-1276 (2011).)
- Mg: green, Si: yellow, Al: blueish, O: red
- MgO6 octahedra (green), Si/AlO4 tetrahedra (yellow)
- Reference: Crystal structure of a two-layer Mg-vermiculite
H. Shirozu, S.W. Bailey
American Mineralogist (1966) 51 (7): 1124-1143.
For a 3D interactive version on sketchfab, see here: