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Ankerite

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Matthias Joseph Anker
Formula:
Ca(Fe2+,Mg)(CO3)2
Usually contains large amounts of Mg and sometimes Mn.
View Commodity Page:
Colour:
Brown, white to grey, yellowish-brown, tan, fawn, greenish.
Lustre:
Pearly
Hardness:
3½ - 4
Specific Gravity:
2.93 - 3.10
Crystal System:
Trigonal
Member of:
Name:
Named after Mathias J. Anker (1771-1843), Styrian (Austria) mineralogist. Originally considered to be Ca(Mg,Fe)(CO3)2 (eg. Hey, 1955, with >10% FeCO3) with no specific requirement for Fe>Mg, before being redefined as strictly having Fe>Mg, i.e. with the dominant endmember CaFe(CO3)2. It was commonly given the end-member formula Ca2FeMg(CO3)4; Hey (1955) actually used the name ferrodolomite for CaFe(CO3)2. The redefinition of the name means the majority of old specimens labelled "ankerite" are now considered to be ferroan dolomite, and true ankerite is quite rare.
Dolomite Group. Ankerite-Dolomite Series, and the Ankerite-Kutnohorite Series.

Note: Most (unanalysed) "ankerite" specimens are actually Fe-bearing (ferroan) dolomite (Mg>Fe), because of nomenclature changes. The majority of alleged "ankerite" photos here actually depict Fe-rich dolomite (except for a relatively few analytically confirmed ankerites). Even the old so-called "type locality ankerite" from Erzberg, Styria, would not quite fit the modern definition, with analysis showing (Mg 0.520, Fe 0.457, Mn 0.021) apfu (Schoklitsch, K. (1935) Zeit. Krist., 90, 433 - taken from DHZ).

The end-member composition CaFe(CO3)2 with dolomitic structural ordering has neither been synthesized (Goldsmith et al., 1962; Rosenberg, 1967) nor have they been found in nature (Dana's System of Mineralogy, Vol. II, 1951; Deer et al., 1962; Goldsmith et al., 1962; Beran, 1975); compositions reach about 70 mol.% CaFe(CO3)2. Chai and Navrotsky (1996), who synthesised disordered ankerite under high-pressure-high-temperature conditions, considered ordered CaFe(CO3)2 to be non-existent.


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Classification of AnkeriteHide

Approved, 'Grandfathered' (first described prior to 1959)
5.AB.10

5 : CARBONATES (NITRATES)
A : Carbonates without additional anions, without H2O
B : Alkali-earth (and other M2+) carbonates
Dana 7th ed.:
14.2.1.2
14.2.1.2

14 : ANHYDROUS NORMAL CARBONATES
2 : AB(XO3)2
11.13.6

11 : Carbonates
13 : Carbonates of Fe

Physical Properties of AnkeriteHide

Pearly
Transparency:
Translucent
Colour:
Brown, white to grey, yellowish-brown, tan, fawn, greenish.
Streak:
White
Hardness:
3½ - 4 on Mohs scale
Tenacity:
Brittle
Cleavage:
Perfect
Perfect on {1011}
Fracture:
Hackly
Density:
2.93 - 3.10 g/cm3 (Measured)    3.11 g/cm3 (Calculated)
Comment:
density 3.121 for type location material (Ford, 1971)

Optical Data of AnkeriteHide

Type:
Uniaxial (-)
RI values:
nω = 1.690 - 1.750 nε = 1.510 - 1.548
Max Birefringence:
δ = 0.180 - 0.202
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
Moderate
Dispersion:
Strong

Chemical Properties of AnkeriteHide

Formula:
Ca(Fe2+,Mg)(CO3)2

Usually contains large amounts of Mg and sometimes Mn.
IMA Formula:
CaFe2+(CO3)2
Common Impurities:
Mn

Crystallography of AnkeriteHide

Crystal System:
Trigonal
Class (H-M):
3 - Rhombohedral
Space Group:
R3
Cell Parameters:
a = 4.8312(2) Å, c = 16.1663(3) Å
Ratio:
a:c = 1 : 3.346
Unit Cell V:
326.78 ų (Calculated from Unit Cell)
Z:
3
Morphology:
Crystals commonly rhombohedral with {1011} or, less commonly, {4041} dominant.
Twinning:
Simple twins on {0001}, {1010}. {1120}
Comment:
For sample with 68 mol% CaFe(CO3)2 (Reeder & Dollase, 1989). A sample with ca. 70 mol% CaFe(CO3)2 has a = 4.836 and 16.186 A (Ross & Reeder, 1992).

X-Ray Powder DiffractionHide

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Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.
Powder Diffraction Data:
d-spacingIntensity
2.899(100)
1.812(6)
2.199(6)
Comments:
Data from Webmineral, but may not be true ankerite. When Fe>Mg the main(104) peak must be at least 2.910, and even more if you have significant Mn and other substitutions.

Other Language Names for AnkeriteHide

Catalan:Ankerita
Dutch:Ankeriet
French:Ankérite
Hungarian:Ankerit
Italian:Ankerite
Lithuanian:Ankeritas
Polish:Ankeryt
Simplified Chinese:铁白云石
Slovak:Ankerit
Spanish:Ankerita
Swedish:Ankerit
Ukrainian:Анкерит

Varieties of AnkeriteHide

Manganoan AnkeriteA manganese-bearing variety of ankerite.
Nickeliferous AnkeriteA nickel-bearing variety of ankerite.

Relationship of Ankerite to other SpeciesHide

Member of:
Other Members of this group:
DolomiteCaMg(CO3)2Trig. 3 : R3
KutnohoriteCa(Mn,Mg,Fe)(CO3)2Trig. 3 : R3
MinrecorditeCaZn(CO3)2Trig. 3 : R3
NorsethiteBaMg(CO3)2Trig. 3 2 : R3 2
Forms a series with:

Common AssociatesHide

Associated Minerals Based on Photo Data:
Quartz205 photos of Ankerite associated with Quartz on mindat.org.
Calcite130 photos of Ankerite associated with Calcite on mindat.org.
Sphalerite70 photos of Ankerite associated with Sphalerite on mindat.org.
Pyrite48 photos of Ankerite associated with Pyrite on mindat.org.
Fluorite47 photos of Ankerite associated with Fluorite on mindat.org.
Galena44 photos of Ankerite associated with Galena on mindat.org.
Chalcopyrite41 photos of Ankerite associated with Chalcopyrite on mindat.org.
Siderite41 photos of Ankerite associated with Siderite on mindat.org.
Rutile15 photos of Ankerite associated with Rutile on mindat.org.
Baryte15 photos of Ankerite associated with Baryte on mindat.org.

Related Minerals - Nickel-Strunz GroupingHide

5.AB.05CalciteCaCO3Trig. 3m (3 2/m) : R3c
5.AB.05GaspéiteNi(CO3)Hex.
5.AB.05MagnesiteMgCO3Trig. 3m (3 2/m) : R3c
5.AB.05OtaviteCdCO3Trig. 3m (3 2/m)
5.AB.05RhodochrositeMnCO3Trig. 3m (3 2/m) : R3c
5.AB.05SideriteFeCO3Trig. 3m (3 2/m) : R3c
5.AB.05SmithsoniteZnCO3Trig. 3m (3 2/m) : R3c
5.AB.05SpherocobaltiteCoCO3Trig. 3m (3 2/m) : R3c
5.AB.10DolomiteCaMg(CO3)2Trig. 3 : R3
5.AB.10KutnohoriteCa(Mn,Mg,Fe)(CO3)2Trig. 3 : R3
5.AB.10MinrecorditeCaZn(CO3)2Trig. 3 : R3
5.AB.15AragoniteCaCO3Orth. mmm (2/m 2/m 2/m)
5.AB.15CerussitePbCO3Orth. mmm (2/m 2/m 2/m)
5.AB.15StrontianiteSrCO3Orth. mmm (2/m 2/m 2/m)
5.AB.15WitheriteBaCO3Orth. mmm (2/m 2/m 2/m)
5.AB.20VateriteCaCO3Hex. 6/mmm (6/m 2/m 2/m) : P63/mmc
5.AB.25HuntiteCaMg3(CO3)4Trig. 3 2 : R3 2
5.AB.30NorsethiteBaMg(CO3)2Trig. 3 2 : R3 2
5.AB.35AlstoniteBaCa(CO3)2Tric.
5.AB.40OlekminskiteSr(Sr,Ca,Ba)(CO3)2Trig.
5.AB.40ParalstoniteBaCa(CO3)2Trig.
5.AB.45BarytocalciteBaCa(CO3)2Mon. 2/m : P21/m
5.AB.50Carbocernaite(Ca,Na)(Sr,Ce,Ba)(CO3)2Orth. mm2
5.AB.55BenstoniteBa6Ca6Mg(CO3)13Trig. 3 : R3
5.AB.60JuangodoyiteNa2Cu(CO3)2Mon. 2/m : P21/b

Related Minerals - Dana Grouping (8th Ed.)Hide

14.2.1.1DolomiteCaMg(CO3)2Trig. 3 : R3
14.2.1.3KutnohoriteCa(Mn,Mg,Fe)(CO3)2Trig. 3 : R3
14.2.1.4MinrecorditeCaZn(CO3)2Trig. 3 : R3

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

11.13.1SideriteFeCO3Trig. 3m (3 2/m) : R3c
11.13.2PyroauriteMg6Fe3+2(OH)16[CO3] · 4H2OTrig. 3m (3 2/m) : R3m
11.13.3Pyroaurite-2HMg6Fe3+2(OH)16(CO3) · 4H2OHex. 6/mmm (6/m 2/m 2/m) : P63/mmc
11.13.4BrugnatelliteMg6Fe3+(CO3)(OH)13 · 4H2OHex.
11.13.5CoalingiteMg10Fe3+2(OH)24[CO3] · 2H2OTrig.

Other InformationHide

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Ankerite in petrologyHide

References for AnkeriteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Mohs, F. (1825) Paratomous lime-haloide. in Treatise on Mineralogy Vol II, translated by Haidinger, Archibald and Co. (Edinburgh), 100-101.
Mohs, F. (1825) Characters of the genera and species of the orders of class II. I. Order. Haloide. V. Lime-haloide. 4. Paratomous. Ankerite. in: Treatise on Mineralogy Vol I, translated by Haidinger, Archibald and Co. (Edinburgh), 411-411.
Luboldt, R. (1857) Ueber den Ankerit. Annalen der Physik: 178: 435-437.
Ford, W.E. (1917) Studies in the Calcite Group. In: Transactions of the Connecticut Academy of Arts and Sciences 22:211-248 (October 1917).
Rocza (1926) Zentralblatt Mineralien: 229.
Winchell (1927) part 2: 75.
Larsen, E.S., Berman, H. (1934) The Microscopic Determination of the Nonopaque Minerals, Second edition, USGS Bulletin 848: 229.
Palache, C., Berman, H., Frondel, C. (1951) The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged: 208-217.
Goldsmith, J.R., Graf, D.L., Witters, J., Northrop, D.A. (1962) Studies in the system CaCO3•MgCO3•FeCO3: (1) Phase relations; (2) A method for major element spectrochemical analyses; and, (3) Composition of some ferroan dolomites. Journal of Geology: 70: 659-688.
Beran, A., Zemann, J. (1977) Refinement and comparison of the crystal structures of a dolomite and of an Fe-rich ankerite. Tschermaks Mineralogische und Petrographische Mitteilungen 24: 279-286.
Reeder, R., Dollase, W. (1989) Structural variation in the dolomite-ankerite solid-solution series: An X-ray, Mössbauer, and TEM study. American Mineralogist: 74: 1159-1167.
Walmsley, J.C., Lang, A.R. (1992) On submicrometer inclusions in diamond coat: Crystallography and composition of ankerites and related rhombohedral carbonates. Mineralogical Magazine: 56: 533-543.
Ross, N.L., Reeder, R. (1992) High-pressure structural study of dolomite and ankerite. American Mineralogist: 77: 412-421.
Chai, L., Navrotsky, A. (1996) Synthesis, characterization, and energetics of solid solution along the dolomite-ankerite join, and implications for the stability of ordered CaFe(CO3)2. American Mineralogist: 81: 1141-1147.
Hilscher, G., Rogl, P., Zemann, J., Ntaflos, T. (2005) Low-temperature magnetic investigation of ankerite. European Journal of Mineralogy: 17: 103-105.
Rividi, N., van Zuilen, M., Philippot, P., Ménez, B., Godard, G., Poidatz, E. (2010) Calibration of carbonate composition using micro-Raman analysis: Application to planetary surface exploration. Astrobiology: 10: 293-309.

Internet Links for AnkeriteHide

Localities for AnkeriteHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListShow