Coloradoite
Encyclopedia
Coloradoite, also known as mercury telluride (HgTe), is a rare telluride
ore associated with metallic deposit (especially gold
and silver
). Gold usually occurs within tellurides (e.g. Coloradoite) as a high finess native-metal (Fadda et al., 2005).
The quest for mining led to the discovery of telluride ores which were found to be associated with metals. Tellurides are ingrown into ores containing these precious metals and are also responsible for a significant amount these metals being produced. Coloradoite a member of the coordination subclass of tellurides is a covalent compound that is isostructural
with sphalerite
(ZnS) (Povarennykh, 1972). Its chemical properties are highly instrumental in distinguishing it from other tellurides. First discovered in Colorado in 1877, other deposits containing coloradoite have been discovered since then. Although it plays an important role in the geology of minerals, it can also be used for other purposes.
and subsequently other telluride ores were found in other parts of the world (Mark and Scibird, 1908). The first discovery and description of coloradoite
was by Frederick Augustus Genth
in the Boulder veins of Colorado
in 1877 (Kelly and Goddard, 1969) and so named after the place of discovery. Other studies have reported its occurrence in other mines of the region and also in mines of the world's significant telluride locations. First classified in the 02 class of minerals by James Dana (Dana, 1904), its classification number is 02.08.02.05. It is also has a Strunz classification
of 02.CB.05a, as a metal sulfide
with gold, silver, iron, copper and other metals (Strunz and Nickel, 2001).
with the general formula AX.
, which could be explained by the presence of metallic bonding in the crystal. Its specific gravity
is 8.10 and is an opaque mineral with colors iron-black inclining to gray; in polished sections, and white with slight grayish brown tint, tarnishing to dull purple. Its fracture
is uneven to subconchordial with a cell length of 6.44 angstrom
s (Anthony et al., 1990). For ease of identification, its etching tests are as follows; With HNO3 it slowly produces a weak brown variegated deposit that acts as a protector to the surface and can be removed completely; with Aqua regia
it effervesces and produces a weak deposit that can be rubbed off and white, radiating spherules are formed, reaction with FeCl3 yields a browning of the surface at different rates and produces black rims of droplet (Ramdohr, 1980). Reactions with HCl, KCN, KOH and HgCl2 yield no precipitates or residue as opposed to petzite
which turns dark brown with HNO3 (Ramdohr, 1980).
Telluride (chemistry)
The telluride ion is Te2−. It is the final stable member of the series of dianions O2−, S2−, and Se2− ....
ore associated with metallic deposit (especially gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
and silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
). Gold usually occurs within tellurides (e.g. Coloradoite) as a high finess native-metal (Fadda et al., 2005).
The quest for mining led to the discovery of telluride ores which were found to be associated with metals. Tellurides are ingrown into ores containing these precious metals and are also responsible for a significant amount these metals being produced. Coloradoite a member of the coordination subclass of tellurides is a covalent compound that is isostructural
Isostructural
The term isostructural is used for chemical compounds that have similar chemical structures, and also with the meaning of isomorphous when used in relation to crystal structures...
with sphalerite
Sphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...
(ZnS) (Povarennykh, 1972). Its chemical properties are highly instrumental in distinguishing it from other tellurides. First discovered in Colorado in 1877, other deposits containing coloradoite have been discovered since then. Although it plays an important role in the geology of minerals, it can also be used for other purposes.
Introduction
Telluride ores occur mainly with metal deposits. In 1848, C.T. Jackson was the first to discover an American mineral containing the element tellurium in the Whitehall mine, in Spotsylvania County, near Frederickson, VA. (Kemp, 1898). Tellurides of gold were first discovered in 1782 in TransylvaniaTransylvania
Transylvania is a historical region in the central part of Romania. Bounded on the east and south by the Carpathian mountain range, historical Transylvania extended in the west to the Apuseni Mountains; however, the term sometimes encompasses not only Transylvania proper, but also the historical...
and subsequently other telluride ores were found in other parts of the world (Mark and Scibird, 1908). The first discovery and description of coloradoite
Coloradoite
Coloradoite, also known as mercury telluride , is a rare telluride ore associated with metallic deposit . Gold usually occurs within tellurides as a high finess native-metal ....
was by Frederick Augustus Genth
Frederick Augustus Genth
Frederick Augustus Ludwig Karl Wilhelm Genth was a United States chemist.-Biography:...
in the Boulder veins of Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
in 1877 (Kelly and Goddard, 1969) and so named after the place of discovery. Other studies have reported its occurrence in other mines of the region and also in mines of the world's significant telluride locations. First classified in the 02 class of minerals by James Dana (Dana, 1904), its classification number is 02.08.02.05. It is also has a Strunz classification
Strunz classification
Nickel–Strunz classification is a scheme for categorizing minerals based upon their chemical composition, introduced by German mineralogist Karl Hugo Strunz in his 1941 Mineralogische Tabellen. The 4th edition was edited by Christel Tennyson too . It was followed by A.S...
of 02.CB.05a, as a metal sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
with gold, silver, iron, copper and other metals (Strunz and Nickel, 2001).
Composition
The chemical formula for coloradoite is HgTe. Theoretically the composition (%) of HgTe is Hg 61.14, Te 38.86 (Vlasov, 1966); Table 1 shows results from a chemical analyses reported by Vlasov on samples collected from two different locations. Because it is found with other telluride ores, it carries some other metals like gold and silver (Wallace, 1908). In its pure form, it has the composition mentioned above. A little hard to identify, petzite which is hazardous could be mistaken for coloradoite, on the other hand, petzite is anisotropic as opposed to coloradoite being an isotropic mineral(Ramdohr, 1980). It is a binary compoundBinary compound
A binary compound is a chemical compound that contains exactly two different elements. Examples of binary ionic compounds include calcium chloride , sodium fluoride , and magnesium oxide , whilst examples of binary covalent compounds include water , carbon monoxide , and sulfur hexafluoride...
with the general formula AX.
| Table 1. Results of chemical analyses of coloradoite (%) (Vlasov, 1966) | |||||
|---|---|---|---|---|---|
| Components | Kalgoorlie, Western Australia | Lake Shore, Ontario | |||
| Hg | 60.95 | 61.62 | 58.55 | ||
| Pb | - | - | 1.60 | ||
| Te | 39.98 | 38.43 | 39.10 | ||
| Insoluble Residue | - | - | 0.25 | ||
| Total | 100.33 | 100.05 | 99.50 | ||
Structure
Coloradoite has a sphalerite structure also known as the “diamond” or “blende” structure; a face centered cubic array in which Hg2+ are in tetrahedral coordination with Te2-, with a stacking sequence of ABCABC (Klein and Dutrow, 2007). The tetrahedral in the sphalerite group a joined together through their apices and rotated through 60̊ with respect to each other (Stanton, 1972). Figure 1 shows the atomic structure of coloradoite. The structure is a unit cube with the Te2- ions at the corners and face centers. The four mercury atoms are coordinated so that each mercury atom lies at the center of a regular tetrahedron of tellurium atoms and each tellurium lies at the center of a regular tetrahedron of mercury atoms. Its crystal point group of *43m and space group is F*43m (Anthony et al., 1990). It is a covalent compound with a high proportion of metallic bonding, due to its low valencies and even lower interatomic distances (Povarennykh). It is also isotropic, meaning it has just one refractive index.Physical properties
Coloradoite is a brittle, massively granular mineral, with a hardness of 2.5. (Vlasov, 1966) It has a metallic lusterLustre (mineralogy)
Lustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. The word lustre traces its origins back to the Latin word lux, meaning "light", and generally implies radiance, gloss, or brilliance....
, which could be explained by the presence of metallic bonding in the crystal. Its specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
is 8.10 and is an opaque mineral with colors iron-black inclining to gray; in polished sections, and white with slight grayish brown tint, tarnishing to dull purple. Its fracture
Fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
is uneven to subconchordial with a cell length of 6.44 angstrom
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
s (Anthony et al., 1990). For ease of identification, its etching tests are as follows; With HNO3 it slowly produces a weak brown variegated deposit that acts as a protector to the surface and can be removed completely; with Aqua regia
Aqua regia
Aqua regia or aqua regis is a highly corrosive mixture of acids, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and hydrochloric acid, usually in a volume ratio of 1:3, respectively...
it effervesces and produces a weak deposit that can be rubbed off and white, radiating spherules are formed, reaction with FeCl3 yields a browning of the surface at different rates and produces black rims of droplet (Ramdohr, 1980). Reactions with HCl, KCN, KOH and HgCl2 yield no precipitates or residue as opposed to petzite
Petzite
The mineral petzite, Ag3AuTe2, is a soft, steel-gray telluride mineral generally deposited by hydrothermal activity. It forms isometric crystals, and is usually associated with rare tellurium and gold minerals, often with silver, mercury, and copper....
which turns dark brown with HNO3 (Ramdohr, 1980).
Geologic occurrence
Coloradoite was first discovered in 1877 by F.A Genth, from the Smuggler mine at Balarat and the Keystone and Mountain Lion mines of the Magnolia district in Colorado, USA ( Kelly and Goddard, 1969); it was named after the state it was found in. Later studies showed its existence in other mines of the region as well as Kalgoorlie, Australia and Kirkland Lake District, Canada (Bateman, 1956). It is found in large quantities in ores made up of intergrown tellurium, calverite or sylvanite, melonite and altaite, as anhedral grains either enclosed in single crystals of tellurium or localized along grain boundaries in tellurium aggregates, among others (Kelly and Goddard, 1969). The tectonic settings for ore deposits are; (a) Magmatic deposits (Waarkraal, South Africa) (b) Contact metasomatic ( Nickel Plate mine, British Columbia, (c) Lode and Massive replacement deposits ( Kirkland Lake , Ontario and South Dakota respectively), and (d) Cavity filling (Cripple Creek , Colorado, Kalgoorlie, Australia) (Bateman, 1956). Tellurides are accountable for just about 20% of gold production and gold mineralization is hosted chiefly by Archean-aged dolerites and basalts that have been metamorphosed to the greenschist facies. This mineralization occurs in hundreds of auriferous and telluride-bearing lodes (Shackleton et al., 2003).External links
- Coloradoite at WebElements.com