Mineral Information and Data:

Ankerite
CaFe2+(CO3)2 [CNMNC approved formula]

Named for Mathias Joseph Anker (1771-1843), Austrian mineralogist.

IMA status : Valid species (Pre-IMA 1825) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
14.02.01.02  
  (14) Anhydrous Carbonates
  (14.02) with Compound Formula A+ B++ (CO3)2
  (14.02.01) Dolomite Group (Trigonal: R-3)
  
Nickel-Strunz
(10th edition) :
05.AB.10
  (05) Carbonates and Nitrates
  (05.A) Carbonates without additional anions, without H2O
  (05.AB) Alkali-earth (and other M2+) carbonates
  
Crystal system: Trigonal System
Point group (H-M): 3 — rhombohedral
Unit cell: a = 4.82 Å, c = 16.13 Å
Crystal Habit: Crystals simple rhombohedrons; massive, fine to coarse granular
Twinning: Common on {0001}, {1010}, or {1120}
  
Color: White, Grey, yellowish brown to brown
Diaphaneity: Translucent to opaque
Luster: Vitreous to pearly
Hardness (Mohs): 3.5 to 4
Measured Density: 2.97 to 3 g/cm3
Cleavage: 1; {10-11}perfect
Tenacity: Brittle
Fracture: Subconchoidal
Streak: White
  
Polymorphism and Series: Forms two series, with dolomite and with kutnohorite.
Geologic Setting: 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.
Mineral Association: Siderite, dolomite
  
Synonyms/varieties: Tautoklin

 

Ankerite
Ankerite crystals to 6 mm
Origin: Nant Helen opencast coal mine, Onllwyn, Neath-Port Talbot (West Glamorgan; Glamorgan), Wales, UK
Photo and Owner: Steve Rust

 

Ankerite
Origin: Formazza Valley, Piedmont, Italy
Sample size: 3.5 x 2.5 x 2.8 cm
Photo: Dan Weinrich

 

Ankerite
(zoom-in of above)

 

Ankerite
Origin: Bou Bekker, Morocco
Sample size: 13.7 x 9.6 x 5.9 cm
Photo: Rob Lavinsky

 

Ankerite
(zoom-in of above)

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