ANKERITE
- Chemistry: Ca(Fe, Mg, Mn)(CO3)2, Calcium Iron Magnesium Manganese Carbonate
- Class: Carbonates
- Group: Dolomite
Ankerite is a member of the Dolomite Group of minerals. Like dolomite, (CaMg(CO3)2) the structure of ankerite consists of alternating layers of carbonate groups (CO3) and layers of metal cations. To add complexity, the cation layers alternate between calcium and iron. This alternation has the effect of lowering the symmetry of the crystals to only bar 3. Without this ordered alternation of metal ions, ankerite's symmetry would be the same as calcite's symmetry, bar 3 2/m. Dolomite, siderite and ankerite share many similarities and are often confused for each other. Ankerite however is usually more dense, opaque and deeply colored than dolomite; but not as much as siderite.
The conversion of calcite to dolomite has troubled sedimentologists and as yet has not been adequately explained. The puzzle has often been called "The Dolomite Problem" and a mechanism is needed to explain the large deposits of dolomite rock found around the world. Some sedimentologists believe that ankerite may be a short-lived intermediate in a transformation between calcite (CaCO3) and dolomite. It is chemically and crystallographically easier to explain a transformation from calcite to ankerite to dolomite; than it is to explain the transformation from calcite to dolomite. But the diffinitive answer is still unknown.
PHYSICAL CHARACTERISTICS:
- Color is off-white, brown and gray; also yellow to orange.
- Luster is vitreous to pearly.
- Transparency: Crystals are commonly translucent.
- Crystal System is trigonal; bar 3.
- Crystal Habits generally are curved rhombohedral, can also be compact, granular and massive.
- Cleavage is perfect in three directions, forming rhombs.
- Fracture is conchoidal.
- Hardness is 3.5 - 4
- Specific Gravity is 3.0 - 3.1 (average).
- Streak is white.
- Other Characteristics: Indices of refraction are 1.54 and 1.73. Crystals tend to be brittle and will dissolve in hydrochloric acid with some effervescence.
- Associated Minerals include sulfide ores such as pyrrhotite, sphalerite and galena and other carbonates such as calcite, dolomite, rhodochrosite and siderite. Also found with quartz, albite and chlorite.
- Notable Occurrences include the type locality of Styria, Austria as well as the Homestake Mine, South Dakota and Calaveras County, California, USA; Chuhuahua, Mexico; Australia; New Zealand; Hungary; England; Transvaal, South Africa; Peru and Eastern Canada.
- Best Field Indicators are its crystal habit, hardness, cleavage, color and associations.
 Amethyst Galleries' Mineral Gallery MINERALS |
ANKERITE specimen ank-1
$ 15.00
$ 15.00
Dims: 1.75" x 1.63" x 1"(4.4 x 4.1 x 2.5 cm)
Wt: 1.17 oz.(33.3 g)
Carson Hill Mine, Calaveras County, California, U.S.A.
This specimen is composed almost entirely of Ankerite, a mineral that is basically a cross between calcite and siderite. It is in the form of thin fan-shaped, bladed crystals that measure up to 3/4"(1.9 cm) wide and 1/2"(1.3 cm) high. They are off-white in color and have a pearly to silky luster due to subtle but concentrated patterns on their faces. The specimen feels surprisingly heavy for its size- I'll have to ask David about the specific gravity. Even though the blades appear delicate, there is little damage to them except for some that are at the edge of the piece and one that was cleaved near its base. This is a pretty little specimen, even with the dull color- I like the luster of it best of all.
ank-1 ($ 15.00)
Carson Hill Mine, Calaveras County, California, U.S.A.
ANKERITE specimen ank-2
$ 55.00
$ 55.00
Dims: 3.88" x 1.5" x 2"(9.7 x 3.8 x 5.1 cm)
Wt: 6.47 oz.(183.4 g)
Carson Hill Mine, Calaveras County, California, U.S.A.
There are at least 20 flat, wide blades of Ankerite on this specimen. They have a uniform, off-white coloration and a pearly to satiny luster caused by thousands if tiny growth striations that cover each of their faces. There is considerable damage to the cluster, mostly limited to the edges of the specimen. They are translucent but slightly cloudy and hava a maximum size of 3/4"(1.9 cm) width and 1/2"(1.3 cm) height. These rest on a bed that seems to be a mixture of quartz and either an earlier growth of Ankerite with considerable rust staining, or Dolomite, it's very hard to tell. The quartz crystals are small in comparison to the Ankerites and are clear but heavily internally fractured, and several are shattered and incomplete. All of this rests on a bed of massive quartz.
ank-2 ($ 55.00)
Carson Hill Mine, Calaveras County, California, U.S.A.
ANKERITE specimen ank-3
$ 30.00
$ 30.00
Dims: 2.19" x 1.88" x 1.25"(5.6 x 4.8 x 3.2 cm)
Wt: 3.34 oz.(94.8 g)
Carson Hill Mine, Calaveras County, California, U.S.A.
I really do hope that this particular specimen sells quickly, because it's already caused me a lot of trouble just to find out exactly what it is made of! First, there are at least 20 thin, broad, curved blades of yellow Ankerite, which have moderate damage and a good, pearly luster. They measure an average 1/4"(6 mm) in length and half of that in height, and are translucent. The Ankerites rest on a bed of surprisingly clear quartz crystals that also have moderate damage, a good sparkle, and good form. The quartz crystals also average about 1/4"(6 mm) and rest on a bed ofquartz and maybe calcite intermixed with mariposite. I searched and finally found the book that would tell me if it even existed, looked it up, and found that it is a chromic variety of phengite. I looked that up, and found that 'phengite' is a silica-rich variety of muscovite! Needless to say, it is green. Somebody, please buy this and put it out of my misery!
ank-3 ($ 30.00)
Carson Hill Mine, Calaveras County, California, U.S.A.
ANKERITE specimen ank-4
$ 75.00
$ 75.00
Dims: 3.3" x 2.7" x 2.6"(8.4 x 6.9 x 6.6 cm)
Wt: 11.7 oz.(331 g)
Gilman, Colorado, U.S.A.
Approximately 20 rhombohedral Ankerite crystals rest on the sphalerite base of this specimen. They range in size from 2 mm to almost 0.5" (1.3 cm) in all dimensions and show a noticeable but small amount of damage. The crystals have a creamy color and pearly to waxy luster. They show a dull translucence, but damage to some of the crystals has exposed their colorless, transparent cores; only a thin layer around each crystal is translucent. These crystals are intergrown with hundreds of dark sphalerites that make up the bulk of the piece. These sphalerites occur in what appears to be a tetragonal form, though intergrowth tends to warp their shapes, and do not exceed 0.3" (8 mm) in diameter. Twinning is visible in several crystals. They have a black color, adamantine luster, and are thoroughly opaque. Besides these two minerals, there is no other material or host rock present on the specimen.
ank-4 ($ 75.00)
Gilman, Colorado, U.S.A.
ANKERITE specimen ank-5
$ 30.00
$ 30.00
Dims: 2.3" x 1.6" x 1.4" (5.8 x 4.1 x 3.6 cm)
Wt: 2.53 oz. (71.8 g)
Carson Hill Quarry, Calaveras County, California, U.S.A.
At least 20 rounded Ankerite blades make up the bulk of this specimen. Though at least half of them are damaged or broken, those that are complete show an excellent and very delicate form. The largest crystal has a diameter of nearly 0.5" (1.3 cm) and like the others, possesses very sharp edges and finely but intensely striated faces that give it a silky luster. All of the crystals have a cream coloration and a milky consistency that renders them only dimly transparent along their edges. This effect is also aided by the presence of some internal fractures that lie within most of the crystals. Among the Ankerites rests a single hexagonal prismatic quartz crystal that is colorless and has excellent form. It is transparent and very clear in the upper two-thirds of its length. Below that, it shows intense cloudiness due to inclusions. All of this rests on a base that consists mostly of broken, intergrown Ankerites. However, there are a few other bits of material present; a dull brown material provides a thin shelf on which the quartz crystal rests. I think that it may be siderite. There are also a few tiny smatterings of a green material present. Judging from its softness and its luster, I am guessing that it is made up of fuchsite or some other mica-related mineral.
ank-5 ($ 30.00)
Carson Hill Quarry, Calaveras County, California, U.S.A.
ANKERITE specimen ank-6
$ 25.00
$ 25.00
Dims: 2.0 x 1.4 x 0.7" (5.1 x 3.5 x 1.7 cm)
Wt: 19 g
Carson Hill Mine, Calaveras County, California, U.S.A.
At least 20 sharp Ankerite blades rest on the crystalline quartz base of this small hand specimen. The crystals do not generally exceed 0.5" (1.3 cm) in diameter or 0.1" (3 mm) in thickness and are in good condition- a few are cleaved, but most are intact. Their trigonal bladed form is somewhat warped- though some faces are well-defined, their outlines are usually odd and not hexagonal in shape. All have a pale cream coloration with a yellow tinge and a bright pearly luster, and are cloudy and dimly transparent at best. The base on which they rest is made up of many small, intergrown quartz crystals that are in very good condition and have excellent form.
ank-6 ($ 25.00)
Carson Hill Mine, Calaveras County, California, U.S.A.
ANKERITE specimen ank-7
$ 36.00
$ 36.00
Dims: 1.6 x 1.3 x 1.1" (4.0 x 3.2 x 2.8 cm)
Wt: 1.0 oz. (27 g)
Wake County, North Carolina, U.S.A.
A small cluster of intersecting Ankerites rest on the apparent granite base of this thumbnail specimen. The largest crystal has dimensions of 0.9 x 0.7 x 0.7" (2.5 x 1.8 x 1.8 cm) and appears to be the only complete crystal, though it is still lightly damaged. All have excellent rhombohedral form, however, and a pale, dirty-brown color and pearly luster on their intact faces- damage reveals their milky-white, translucent interiors. The base rock looks much like a granite, but is more likely a syenite- either way, it seems to be an unusual association.
ank-7 ($ 36.00)
Wake County, North Carolina, U.S.A.
ANKERITE specimen ank-8
$ 38.00
$ 38.00
Dims: 3.7 x 3.5 x 2.4" (9.5 x 8.8 x 6.2 cm)
Wt: 1 lb., 3.3 oz. (548 g)
Julcani Mine, Huancavelica Department, Peru
A thick crust of heavily-intergrown Ankerite crystals rests on the dark limestone base of this specimen. The crystals that make up the crust are in very good condition, showing little damage, and reach diameters of 0.6" (1.5 cm). Their rhombohedral form is good, with curved faces and edges- many are tabular, and intergrown back-to-back into "stacks". All have a dull, pale-brown color and a dull greasy luster, and are essentially opaque. Scores of tiny, black crystals are embedded into their surfaces- I think that these are sphalerites.
ank-8 ($ 38.00)
Julcani Mine, Huancavelica Department, Peru
ANKERITE specimen ank-9
$ 34.00
$ 34.00
Dims: 3.5 x 1.8 x 1.4" (8.9 x 4.5 x 3.5 cm)
Wt: 5.9 oz. (167 g)
Rooiberg Mine, Transvaal, Republic of South Africa
This small cabinet specimen is made up mostly of Ankerite blades that have intergrown to form a crust. These blades are generally in good condition and reach 0.4" (1 cm) in diameter. Their trigonal bladed form is rather warped due to intense intergrowth but is still discernable. Their color is very difficult to assess, as rust has stained the material intensely. A few exposed faces show a pearly luster and a noticeable iridescence. Given the amount of iron oxide present, one would think that the crystals would actually be made of siderite, but they are not dense enough.
ank-9 ($ 34.00)
Rooiberg Mine, Transvaal, Republic of South Africa
ANKERITE specimen ank-10
$ 25.00
$ 25.00
Dims:1.0x0.8x0.7" (2.5x2.0x1.8 cm)
Wt: 0.4oz. (10g)
Mt St Hilaire, Quebec, Canada
This specimen consists of a large (0.6", 1.5cm) rhombohedron of ankerite with a small amount of matrix material. The matrix material is white, fibrous, radiating sprays that I believe to be natrolite. On these sprays of natrolite are other tiny ankerite crystals. There are also traces of a silvery metallic mineral, possibly a sulfide of some sort. Traces of black material appear to be manganese oxides. There is no damage to this specimen.
ank-10 ($ 25.00)
Mt St Hilaire, Quebec, Canada