Sarabauite (sar-a-bau'-ite) is a red

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

sulfide mineral with the chemical formula: CaSb₁₀O₁₀S₆.

Origin of name and type locality

Sarabauite was first described in 1977 and named for its type locality, the Sarabau Mine (Lucky Hill mine) in

Sarawak Sarawak (; ) is a States and federal territories of Malaysia, state of Malaysia. The largest among the 13 states, with an area almost equal to that of Peninsular Malaysia, Sarawak is located in northwest Borneo Island, and is bordered by the M ...

Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...

.“Sarabauite” on Mindat.org Accessed 3 December 2010.
/ref> It has also been reported from the

Castelo Branco District Castelo Branco District ( pt, Distrito de Castelo Branco ) is located in Central Portugal. Its capital is Castelo Branco, Portugal, Castelo Branco, which is now also its most populous city, overtaking Covilhã, which was once the largest city, in ...

Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...

Crystallography

Sarabauite is a

mineral.Nakai, I., Adachi, H., Akira Kato, S.M., and Nagashima, K. (1978) 'Sarabauite a new oxide sulfide mineral from the Sarabau mine, Sarawak, Malaysia. American Mineralogist, 63, 715-719. Monoclinic minerals have three crystallographic axes of unequal length. Two of the inter-axial angles are 90 degrees, while the third angle, between the optic axis and the plane containing the other two axes, is unequal to the other inter-axial angles. The monoclinic system includes crystal classes with a single twofold rotation axis and/or a mirror plane. Sarabauite is of the 2/m crystal class; it has a 2 fold rotation axis perpendicular to a mirror plane.Klein, C., and Dutrow, B. (2007) The 23 Edition of the Manual of Mineral Science, 675 p. John Wiley and Sons, Inc. Hoboken, New Jersey, U.S.A.

Optical properties

Sarabauite is a biaxial negative mineral. All minerals of the monoclinic, orthorhombic, and triclinic systems are biaxial minerals. Unlike uniaxial minerals, biaxial crystals have 2 optic axes. This means they have two directions in which light can travel without birefringence, three principal axes, and accordingly three different indices of refraction. Biaxial minerals are further subdivided by optic sign. The optic angle, 2V, is the angle between the two optic axes that is split by the direction of the lowest index of refraction. If 2V is acute, the mineral is biaxial positive. In sarabauite crystals this angle is obtuse, thus the mineral is biaxial negative.

Geologic setting

The

mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...

region that contains the Sarabau Mine is part of the Sumatra Orogen. The region consists of a system of faults and joints through which hydrothermal fluids responsible for the mineralization of sarabauite rise into the overlying carbonate rock.

Mineral importance

Sarabauite is a notable mineral for its

antimony Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient time ...

content, fluid inclusions, accompaniment of

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...

, and its two-stage hydrothermal formation process. The Sarabau Mine is a gold and antimony mine. Sarabauite can be found there in mineral

veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...

through altered

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

containing

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

, wollastonite,

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

, stibnite and senarmonite. Both temperature and fluids are responsible for its formation through a two-stage hydrothermal mineralization process. First, wollastonite, diopside, and

epidote Epidote is a calcium aluminium iron sorosilicate mineral. Description Well developed crystals of epidote, Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly prismatic in habi ...

form at temperatures over 400 °C. In the second stage, at over 377 °C, sarabauite and

native gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...

develop. Calcite, stibnite, and senarmontite also form during the second stage as the mineralization cools further to 377–194 °C. Sarabauite's formation makes it the only hypogene antimony mineral whose fluid inclusions can be studied in thin section under normal light.Dill, H.G., and Horn, E.E. (1996) The origin of a hypogene sarabauite-calcite mineralization at the Lucky Hill Au-Sb mine Sarawak, Malaysia. Journal of Southeast Asian Earth Sciences, 14, 29-35.

References

{{Reflist Sulfosalt minerals Antimony minerals Monoclinic minerals Minerals in space group 15