Barbertonite is a

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

carbonate mineral Carbonate minerals are those minerals containing the carbonate ion, . Carbonate divisions Anhydrous carbonates *Calcite group: trigonal **Calcite CaCO3 **Gaspéite (Ni,Mg,Fe2+)CO3 **Magnesite MgCO3 **Otavite CdCO3 **Rhodochrosite MnCO3 **Sider ...

with formula of . It is

polymorphous Polymorphism, polymorphic, polymorph, polymorphous, or polymorphy may refer to: Computing * Polymorphism (computer science), the ability in programming to present the same programming interface for differing underlying forms * Ad hoc polymorphism ...

with the mineral

stichtite Stichtite is a mineral, a Carbonate mineral, carbonate of chromium and magnesium; formula Mg6Cr2carbon, Coxygen, O3(Ohydrogen, H)16·4water, H2O. Its colour ranges from pink through lilac to a rich purple colour. It is formed as an alteration pro ...

and, along with stichtite, is an alteration product of

chromite Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of Iron, FeChromium, Cr2Oxygen, O4. It is an oxide mineral belonging to the spinel group. The ...

serpentinite Serpentinite is a metamorphic rock composed predominantly of serpentine group minerals formed by serpentinization of mafic or ultramafic rocks. The ancient origin of the name is uncertain; it may be from the similarity of its texture or color ...

. Barbertonite has a close association with stichtite, chromite, and

antigorite Antigorite is a lamellated, monoclinic mineral in the phyllosilicate serpentine subgroup with the ideal chemical formula of (Mg,Fe2+)3Si2O5(OH)4. It is the high-pressure polymorph of serpentine and is commonly found in metamorphosed serpentin ...

(Taylor, 1973). Mills et al. (2011) presented evidence that barbertonite is a polytype of stichtite and should be discredited as a mineral species.

Barbertonite family group

Barbertonite is a member of the

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A regular hexagon is d ...

sjogrenite group along with manasseite and sjogrenite (

Palache ''(Previously, this page expanded into a family history–now in separate entry: q.v. " Pallache family.")'' The Pallache (see Pallache family for many spellings of name) are a Sephardic Jewish family who originated on the Iberian Peninsula, spr ...

et al., 1944). The

rhombohedral In geometry, a rhombohedron (also called a rhombic hexahedron or, inaccurately, a rhomboid) is a special case of a parallelepiped in which all six faces are congruent rhombus, rhombi. It can be used to define the rhombohedral lattice system, a Ho ...

hydrotalcite group consists of the three minerals:
–

with 3 units of ;
–

hydrotalcite Hydrotalcite, or formerly also völknerite, is a layered double hydroxide (LDH) of general formula ·4, whose name is derived from its resemblance with talc and its high water content. Multiple structures containing loosely bound carbonate ions ...

with 3 units of , and;
– pyroaurite with 3 units of . These two

isostructural Isostructural chemical compounds have similar chemical structures. " Isomorphous" when used in the relation to crystal structures is not synonymous: in addition to the same atomic connectivity that characterises isostructural compounds, isomorphous ...

groups are

in relation to each other (Palache et al., 1944).

Structure

The structure of barbertonite has

brucite Brucite is the mineral form of magnesium hydroxide, with the chemical formula Magnesium, Mg(hydroxyl, OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal Vein (geology), vein mineral in metamorphosed li ...

-like layers alternating with interlayers. Neighboring brucite layers are stacked so that the hydroxyl ions () are directly above one another (Taylor, 1973). In between brucite layers are interlayers containing ions and molecules (Taylor, 1973). Oxygen atoms are accommodated in a single set of sites distributed close to the axes that pass through the hydroxyl ions of adjacent brucite layers (Taylor, 1973).

Geologic occurrence

Barbertonite was first found in the Barberton district in

Transvaal Transvaal is a historical geographic term associated with land north of (''i.e.'', beyond) the Vaal River in South Africa. A number of states and administrative divisions have carried the name ''Transvaal''. * South African Republic (1856–1902; ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

. It can also be found in the Ag-Pb mine in Dumas,

Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

(Anthony et al., 2003). Read and Dixon (1933) stated that the mineral that was found in

Cunningsburgh Cunningsburgh, formerly also known as Coningsburgh ( meaning "King's castle"), is a new hamlet and ancient parish in the south of Mainland, Shetland, Scotland. The hamlet is on the coast, nine miles south south west of Lerwick, about halfway betw ...

Shetland Islands Shetland (until 1975 spelled Zetland), also called the Shetland Islands, is an archipelago in Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the Uni ...

was stichtite but it is now thought to be barbertonite because of the very similar indices of the minerals (Frondel et al. 1941). Barbertonite frequently occurs admixed with its rhombohedral analogue and as an alteration product of chromite in

(Anthony et al. 2003).

Barbertonite family group

Structure

Geologic occurrence

References

Further reading