Vaterite
The least stable calcium-carbonate polymorph — hexagonal μ-CaCO₃, occurring in sediments and shells.
Intro adapted from Wikipedia (CC BY-SA).
Vaterite is an IMA-recognized mineral species in the carbonate class, with the chemical formula Ca(CO₃).
It crystallizes in the hexagonal crystal system (space group Pbnm).
Key properties: Mohs hardness 3; specific gravity 2.54; refractive index 1.601; optically uniaxial.
IMA symbol Vtr, IMA status: approved, named in 1911.
A major constituent of a carbonated calcium silicate hydrogel complex formed from larnite (Ballycraigy, Ireland).
It is found associated with Calcite, aragonite, tobermorite, hydrogarnet, kaolinite (Hatrurim Formation, Israel).
The mineral was named to honor Heinrich Vater (1859–1930), Professor of Mineralogy and Chemistry, Tharandt, Germany.