Ankerite

Ankerite is a calcium, iron, magnesium, manganese carbonate mineral of the group of rhombohedral carbonates with formula: Ca(Fe, Mg, Mn)(CO3)2. In composition it is closely related to dolomite, but differs from this in having magnesium replaced by varying amounts of iron(II) and manganese.Normal ankerite is Ca2MgFe(CO3)4. The crystallographic and physical characters resemble those of dolomite and siderite. The angle between the perfect rhombohedral cleavages is 73° 48', the hardness is 3.5 to 4, and the specific gravity is 2.9 to 3.1. The colour is white, grey or reddish to yellowish brown.
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n. ankerite

n. ankerite

(n.)
A mineral closely related to dolomite, but containing iron.
  

General Information:
 Chemical Formula:
Ca(Fe++,Mg,Mn)(CO3)2
 Composition:
(Molecular Weight = 206.39 gm)
Calcium 19.42 % Ca
Magnesium 3.53 % Mg
Manganese 2.66 % Mn
Iron 16.24 % Fe
Carbon 11.64 % C 
Oxygen 46.51 % O 
 Empirical Formula:
CaFe2+0.6Mg0.3Mn2+0.1(CO3)2
 Name Origin:
Named after the Australian mineralogist, M. J. Anker (1771-1843).
Physical Properties:
 Cleavage:
[1011] Perfect, [1011] Perfect, [1011] Perfect
 Color:
brown, brownish yellow, gray, gray brown, or white.
 Density:
3 - 3.1, Average = 3.05
 Diaphaniety:
Translucent to subtranslucent
 Habits:
Crystalline - Coarse - Occurs as well-formed coarse sized crystals., Massive - Uniformly indistinguishable crystals forming large masses., Granular - Generally occurs as anhedral to s ubhedral crystals in matrix.
 Hardness:
3.5-4 - Copper Penny-Flourite
 Luminescence:
None.
 Luster:
Vitreous (Glassy)
 Streak:
white
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ANKERITE