Atheneite
Encyclopedia
Atheneite is a rare metallic compound
commonly associated with palladium
–gold
deposits. It was discovered in 1974 by A.M. Clark, A.J. Criddle, and E.E. Fejer in the Minas Gerais mine in the town of Itabira
, Brazil
(Clark, 1974). Atheneite was also found in 1982 during a major gold rush at Serra Pelada
in northern Brazil. Since then it has been found in the northern region of Para, Brazil, the northern region of Russia, and the Limpopo
province of South Africa (Cabral, 2002; Trabaev, 1995).
Atheneite has a chemical structure very similar to that of graphite
. Its hexagonal crystal system
contributes to its metallic luster, and its color is indicative of its chemical makeup ((Pd,Hg)3As). Its name is derived from the Greek goddess Pallas Athena for its association with palladium-gold deposits. Not much is known about Atheneite because of its rarity.
in an arsenic grouping. This mineral’s composition parallels that of arsenopalladinite Pd8(As, Sb)3, isomertieite, Pd11Sb2As2, and meritieite-II (Cabral, 2002). According to the American Mineralogist, the mineral was first found in concentrates from gold washings in Brazil with intergrowths of arsenopalladinite (Fleischer, 1974). Iron rich hematite
was also found in intergrowths with atheneite, and is interpreted as being the product of a low temperature, hydrothermal origin.
is P6/mmm. It also has a point group
ing of 6/m 2/m 2/m which concludes that its crystal system is hexagonal. Atheneite actually has a dihexagonal dipyramidal crystal form. This same complex hexagonal structure is also the structural make up of graphite
. This mineral does not extinguish under crossed polars, showing bright anisotropic colors from purple-brown to dark grey (Fleischer, 1974). These birefringence
colors are of the first order. The atomic structure of atheneite is very similar to that of the hexagonal structure carbons that make up graphite, however, the bonds that hold the atoms together in atheneite are much stronger than those of graphite.
is 4.5-5. The absolute hardness scale puts this mineral at a 48. Atheneite also has a density of 10.2 g/cm3. When placed in a reflected light, it gives off a white light with a yellowish hue and shows very weak reflectance pleochroism
in oil (Fleischer, 1974).
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
commonly associated with palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
–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...
deposits. It was discovered in 1974 by A.M. Clark, A.J. Criddle, and E.E. Fejer in the Minas Gerais mine in the town of Itabira
Itabira
Itabira is a Brazilian municipal district and one of the main cities of the state of Minas Gerais. The city belongs to the mesoregion Metropolitana de Belo Horizonte and to the microregion of Itabira....
, Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
(Clark, 1974). Atheneite was also found in 1982 during a major gold rush at Serra Pelada
Serra Pelada
Serra Pelada was a large gold mine in Brazil south of the mouth of the Amazon River. The mine was made famous by the images taken by Sebastião Salgado showing an anthill of workers moving vast amounts of ore by hand...
in northern Brazil. Since then it has been found in the northern region of Para, Brazil, the northern region of Russia, and the Limpopo
Limpopo
Limpopo is the northernmost province of South Africa. The capital is Polokwane, formerly named Pietersburg. The province was formed from the northern region of Transvaal Province in 1994, and initially named Northern Transvaal...
province of South Africa (Cabral, 2002; Trabaev, 1995).
Atheneite has a chemical structure very similar to that of graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
. Its hexagonal crystal system
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
contributes to its metallic luster, and its color is indicative of its chemical makeup ((Pd,Hg)3As). Its name is derived from the Greek goddess Pallas Athena for its association with palladium-gold deposits. Not much is known about Atheneite because of its rarity.
Composition and Geologic Occurrence
Atheneite has the chemical formula of (Pd,Hg)3As which gives it the nomenclature of a palladium arsenideArsenide
Arsenide is an arsenic anion with the charge −3. The trianion is formed by the reduction of arsenic by three electrons. For example heating arsenic powder with excess sodium gives sodium arsenide . The anions have no existence in solution since they are extremely basic...
in an arsenic grouping. This mineral’s composition parallels that of arsenopalladinite Pd8(As, Sb)3, isomertieite, Pd11Sb2As2, and meritieite-II (Cabral, 2002). According to the American Mineralogist, the mineral was first found in concentrates from gold washings in Brazil with intergrowths of arsenopalladinite (Fleischer, 1974). Iron rich hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...
was also found in intergrowths with atheneite, and is interpreted as being the product of a low temperature, hydrothermal origin.
Structure
Atheneite’s space groupSpace group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
is P6/mmm. It also has a point group
Point group
In geometry, a point group is a group of geometric symmetries that keep at least one point fixed. Point groups can exist in a Euclidean space with any dimension, and every point group in dimension d is a subgroup of the orthogonal group O...
ing of 6/m 2/m 2/m which concludes that its crystal system is hexagonal. Atheneite actually has a dihexagonal dipyramidal crystal form. This same complex hexagonal structure is also the structural make up of graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
. This mineral does not extinguish under crossed polars, showing bright anisotropic colors from purple-brown to dark grey (Fleischer, 1974). These birefringence
Birefringence
Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
colors are of the first order. The atomic structure of atheneite is very similar to that of the hexagonal structure carbons that make up graphite, however, the bonds that hold the atoms together in atheneite are much stronger than those of graphite.
Physical Properties
Atheneite, as the derivation of the name suggests, has a metallic luster like that of gold. The color ranges from white/grey to blue/grey tint. Its Mohs hardness scaleMohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...
is 4.5-5. The absolute hardness scale puts this mineral at a 48. Atheneite also has a density of 10.2 g/cm3. When placed in a reflected light, it gives off a white light with a yellowish hue and shows very weak reflectance pleochroism
Pleochroism
Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles with polarized light.- Background :Anisotropic crystals will have optical properties that vary with the direction of light...
in oil (Fleischer, 1974).