Name : Quartz; ankerite Accession Number : GE15703 Part of the Geology collection For more details visit www.aucklandmuseum.com/collections Images released under a CC-BY licence. Auckland Museum 2019 — Photo: Auckland Museum Collections from Auckland, Aotearoa New Zealand · CC BY 2.0
Ankerite
A calcium-iron-magnesium carbonate of the rhombohedral carbonate group, also called brown spar or bitter spar.
Intro adapted from Wikipedia (CC BY-SA).
Ankerite is an IMA-recognized mineral species in the carbonate class, with the chemical formula Ca(Fe²⁺,Mg)(CO₃)₂.
It crystallizes in the hexagonal crystal system (space group R-3). It is a member of the Calcite-Dolomite structural group.
Key properties: Mohs hardness 3.5–4; specific gravity 2.93–3.1; White streak; Vitreous to pearly luster; optically uniaxial.
IMA symbol Ank, grandfathered status — known before the IMA’s founding, named in 1825.
Formed in low-grade metamorphosed ironstones and sedimentary banded iron formations; in carbonatites; authigenic, diagenetic, or the product of hydrothermal alteration of carbonate sediments and in hydrothermal sulfide veins.
It is found associated with Siderite, dolomite.
The mineral was named to honor Professor Matthias Joseph Anker (1772–1843), Austrian mineralogist.