Andradite is a

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

species of the garnet group. It is a

nesosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

, with chemical formula Ca₃Fe₂Si₃O₁₂. Andradite includes three varieties: * '' Colophonite'': a historical variety found in the Scandinavian islands, brownish or reddish in color, often opaque or translucent.''Olga Bortnik''. All about precious stones. ― Moscow: Harvest, 2011. * ''

Demantoid Demantoid is the green gemstone variety of the mineral andradite, a member of the garnet group of minerals. Andradite is a calcium- and iron-rich garnet. The chemical formula is Ca3Fe2(SiO4)3 with chromium substitution as the cause of the deman ...

'': Vivid green in color, one of the most valuable and rare stones in the gemological world. * ''Melanite'': Black in color due to limited substitution of

titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

for iron. Also known as "titanian andradite". Forms a solid solution with morimotoite and schorlomite depending on titanium and iron content.Melanite
Mindat.org * ''Topazolite'': Yellow-green in color and sometimes of high enough quality to be cut into a faceted

gemstone A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewellery, jewelry or other adornments. Certain Rock (geology), rocks (such ...

, it is rarer than demantoid. It was first described in 1868 for an occurrence in

Drammen Drammen () is a city and municipality in Buskerud county, Norway. The port and river city of Drammen is centrally located in the south-eastern and most populated part of Norway. Drammen municipality also includes smaller towns and villages such ...

Buskerud Buskerud () is a Counties of Norway, county and a current electoral district in Norway, bordering Akershus, Oslo, Innlandet, Vestland, Telemark and Vestfold. The region extends from the Oslofjord and Drammensfjorden in the southeast to Hardanger ...

Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...

. Andradite was named after the

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

ian statesman, naturalist, professor and poet José Bonifácio de Andrada e Silva (1763–1838).

Occurrence

It occurs in skarns developed in contact metamorphosed impure

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

s or calcic

igneous rock Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

s; in chlorite

schist Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...

s and

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 ...

s and in alkalic

s (typically titaniferous). Associated minerals include vesuvianite,

chlorite The chlorite ion, or chlorine dioxide anion, is the halite (oxyanion), halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as s ...

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 ha ...

spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , a diminutive form of ''spine,'' in reference to its pointed crystals. Prop ...

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 ...

, dolomite and

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...

. It is found in

Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

, the

Ural Mountains The Ural Mountains ( ),; , ; , or simply the Urals, are a mountain range in Eurasia that runs north–south mostly through Russia, from the coast of the Arctic Ocean to the river Ural (river), Ural and northwestern Kazakhstan.

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

and

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

and in

Dnipropetrovsk Oblast Dnipropetrovsk Oblast (), is an administrative divisions of Ukraine, oblast (province) in simultaneously southern, eastern and central Ukraine, the most important industrial region of the country. It was created on February 27, 1932. Dnipropetro ...

Ukraine Ukraine is a country in Eastern Europe. It is the List of European countries by area, second-largest country in Europe after Russia, which Russia–Ukraine border, borders it to the east and northeast. Ukraine also borders Belarus to the nor ...

. Like the other garnets, andradite crystallizes in the cubic

space group In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...

Iad, with unit-cell parameter of 12.051 Å at 100 K.Thomas Armbruster and Charles A. Geiger (1993):
Andradite crystal chemistry, dynamic X-site disorder and structural strain in silicate garnets
" ''European Journal of Mineralogy'' v. 5, no. 1, p. 59-71. The spin structure of andradite contains two mutually canted equivalent antiferromagnetic sublatticesDanylo Zherebetskyy (2010).
Quantum mechanical first principles calculations of the electronic and magnetic structure of Fe-bearing rock-forming silicates
', PhD Thesis, Universal Publishers/Dissertation.com, Boca Raton, Florida, USA, p. 136. . below the Néel temperature (T_N=11 KEnver Murad (1984):
Magnetic ordering in andradite
" ''American Mineralogist'' 69, no. 7-8; pp. 722–24.). File:Mélanite-Mali.jpg, Black crystals of andradite: melanite

References

External links

{{Jewellery Calcium minerals Iron(III) minerals Garnet gemstones Minerals in space group 230 Titanium minerals Minerals described in 1868

Occurrence

See also

References

External links