ankerite
American Heritage Dictionary:
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an·ker·ite
(ăng'kə-rīt') 
n.
A white, gray, or red iron-rich dolomitic or carbonate mineral, Ca(Fe,Mg,Mn)(CO3)2.
n.
A white, gray, or red iron-rich dolomitic or carbonate mineral, Ca(Fe,Mg,Mn)(CO3)2.
[After Matthias Joseph Anker (1771-1843), Austrian mineralogist.]
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The carbonate mineral Ca(Fe,Mg)(CO3)2, also commonly containing some manganese. The mineral has hexagonal (rhombohedral) symmetry and has the cation-ordered structure of dolomite. The name is applied only to those species in which at least 20% of the magnesium positions are occupied by iron or manganese; species containing less iron are termed ferroan dolomites. The pure compound, CaFe(CO3)2, has never been found in nature and has never been synthesized as an ordered compound. See also Dolomite.
Ankerite is commonly white to light brown, its specific gravity is about 3, and its hardness is about 4 on Mohs scale. See also Carbonate minerals.
Wikipedia on Answers.com:
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Ankerite
| Ankerite | |
|---|---|
 Ankerite on quartz from Peru. |
|
| General | |
| Category | Carbonate mineral |
| Chemical formula | Ca(Fe,Mg,Mn)(CO3)2 |
| Strunz classification | 05.AB.10 |
| Crystal symmetry | Trigonal rhombohedral H-M symbol: (3) Space group: R3 |
| Unit cell | a = 4.8312(2) Å, c = 16.1663(3) Å; Z=3 |
| Identification | |
| Color | Brown, yellow, white |
| Crystal habit | Chrystals rhombohedral with curved faces; columnar, stalactitic, granular, massive |
| Crystal system | Trigonal |
| Twinning | Simple twins on {0001}, {1010}. {1120} |
| Cleavage | Perfect on {1011} |
| Fracture | Subconchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 3.5–4 |
| Luster | Vitreous to pearly |
| Streak | White |
| Diaphaneity | Translucent to transparent |
| Specific gravity | 2.93–3.10 |
| Optical properties | Uniaxial (-) |
| Refractive index | nω = 1.690 - 1.750 nε = 1.510 - 1.548 |
| Birefringence | δ = 0.180 - 0.202 |
| Dispersion | Strong |
| References | [1][2][3] |
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. Forms series with dolomite and kutnohorite.[2]
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 color is white, grey or reddish to yellowish brown.
Ankerite occurs with siderite in metamorphosed ironstones and sedimentary banded iron formations. It also occurs in carbonatites. In sediments it occurs as authigenic, diagenetic minerals and as a product of hydrothermal deposition.[1] It is one of the minerals of the dolomite-siderite series, to which the terms brown-spar, pearl-spar and bitter-spar have been historically loosely applied.
It was first recognized as a distinct species by W. von Haidinger in 1825, and named for Matthias Joseph Anker (1771–1843) of Styria, an Austrian mineralogist.[2]
See also
References
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Wikimedia Commons has media related to: Ankerite |
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.
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The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
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McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.
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Mentioned in
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