Hydrotalcite Locality: Snarum, Modum , Buskerud , Norway ( Locality at mindat.org ) Size: 8.4 x 5.2 x 4.1 cm. Hydrotalcite is a rare hydrated, magnesium, aluminum carbonate and this rich specimen is from the Type Locality - Snarum, Norway. Waxy, talc-like, grayish/whitish hydrotalcite is sculpturally embedded in a matrix of oxidized, yellow-green serpentine. Hydrotalcite is so named for its resemblance to talc. From an older museum collection dating to prior to WW I. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Hydrotalcite
A magnesium-aluminium layered double hydroxide resembling talc in feel — once called völknerite — and archetype of the LDH mineral family.
Intro adapted from Wikipedia (CC BY-SA).
Hydrotalcite is an IMA-recognized mineral species in the carbonate class, with the chemical formula Mg₆Al₂CO₃(OH)₁₆(H₂O)₄.
It crystallizes in the hexagonal crystal system (space group R-3m). It is a member of the Hydrotalcite structural group.
Key properties: Mohs hardness 2; specific gravity 2.03–2.09; White streak; Satiny to greasy or waxy luster; refractive index 1.517; optically uniaxial.
IMA symbol Htc, IMA status: approved, named in 1842.
Found as a secondary mineral in serpentinite.
It is found associated with Manasseite, serpentine, dolomite.
As a HYDROus mineral with a resemblance to talc.