Amphibole is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain SiO
4 tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is Amp. Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, within which are two groups and several subgroups.
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula XY(Si,Al)2O6, where X represents calcium (Ca), sodium (Na), iron or magnesium (Mg) and more rarely zinc, manganese or lithium, and Y represents ions of smaller size, such as chromium (Cr), aluminium (Al), magnesium (Mg), cobalt (Co), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V) or even iron. Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes. They share a common structure consisting of single chains of silica tetrahedra. Pyroxenes that crystallize in the monoclinic system are known as clinopyroxenes and those that crystallize in the orthorhombic system are known as orthopyroxenes.
Armalcolite is a titanium-rich mineral with the chemical formula (Mg,Fe2+)Ti2O5. It was first found at Tranquility Base on the Moon in 1969 during the Apollo 11 mission, and is named for Armstrong, Aldrin and Collins, the three Apollo 11 astronauts. Together with tranquillityite and pyroxferroite, it is one of three new minerals that were discovered on the Moon. Armalcolite was later identified at various locations on Earth and has been synthesized in the laboratory. (Tranquillityite and pyroxferroite were also later found at various locations on Earth). The synthesis requires low pressures, high temperatures and rapid quenching from about 1,000 °C to the ambient temperature. Armalcolite breaks down to a mixture of magnesium-rich ilmenite and rutile at temperatures below 1,000 °C, but the conversion slows down with cooling. Because of this quenching requirement, armalcolite is relatively rare and is usually found in association with ilmenite and rutile, among other minerals.
Serpentine subgroup are greenish, brownish, or spotted minerals commonly found in serpentinite. They are used as a source of magnesium and asbestos, and as decorative stone. The name comes from the greenish colour and smooth or scaly appearance from the Latin serpentinus, meaning "serpent rock".
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 FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr2O4). A substitution of the element aluminium can also occur, leading to hercynite (FeAl2O4). Chromite today is mined particularly to make stainless steel through the production of ferrochrome (FeCr), which is an iron-chromium alloy.
Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orthorhombic system (space group Pbnm) with cell parameters a 4.75 Å (0.475 nm), b 10.20 Å (1.020 nm) and c 5.98 Å (0.598 nm).
Diopside is a monoclinic pyroxene mineral with composition MgCaSi
2O
6. It forms complete solid solution series with hedenbergite and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class. It has two distinct prismatic cleavages at 87 and 93° typical of the pyroxene series. It has a Mohs hardness of six, a Vickers hardness of 7.7 GPa at a load of 0.98 N, and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of nα=1.663–1.699, nβ=1.671–1.705, and nγ=1.693–1.728. The optic angle is 58° to 63°.
Enstatite is a mineral; the magnesium endmember of the pyroxene silicate mineral series enstatite (MgSiO3) – ferrosilite (FeSiO3). The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous and metamorphic rocks. The intermediate composition, (Mg,Fe)SiO
3, has historically been known as hypersthene, although this name has been formally abandoned and replaced by orthopyroxene. When determined petrographically or chemically the composition is given as relative proportions of enstatite (En) and ferrosilite (Fs) (e.g., En80Fs20).
Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the websterites which contain both types of pyroxenes. Closely allied to this group are the hornblendites, consisting essentially of hornblende and other amphiboles.
Diallage is an inosilicate, meaning it's a chain silicate, and is a part of the pyroxene group. Diallage is a junction between augite and diopside, just like fassaite. It was named in 1801 by René Just Haüy. Its name derives from the Greek word diallaghé, as its composition differs from that of the other minerals in the pyroxene group. It is a fairly common mineral, and is cheap.
Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Its chemical formula is (Mg,Fe)SiO3. It is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Many references have formally abandoned this term, preferring to categorise this mineral as enstatite or ferrosilite. It forms a solid solution series with the minerals enstatite and ferrosilite, being a mid-way member between the two. Pure enstatite contains no iron, while pure ferrosilite contains no magnesium; hypersthene is the name given to the mineral when a significant amount of both elements are present. Enstatite is stable at atmospheric pressure, but ferrosilite is stable only at elevated pressure, decomposing into quartz and fayalite at atmospheric pressure unless stabilized by magnesium or other impurities.
Rhodonite is a manganese inosilicate, with the formula (Mn, Fe, Mg, Ca)SiO3, and member of the pyroxenoid group of minerals, crystallizing in the triclinic system. It commonly occurs as cleavable to compact masses with a rose-red color (its name comes from Ancient Greek ῥόδον (rhódon) 'rose'), often tending to brown due to surface oxidation. The rose-red hue is caused by the manganese cation (Mn2+).
Ultramafic rocks are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals. The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.
Norite is a mafic intrusive igneous rock composed largely of the calcium-rich plagioclase labradorite, orthopyroxene, and olivine. The name norite is derived from Norge, the Norwegian name for Norway.
Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group of igneous rocks. Cumulates can be deposited on top of other older cumulates of different composition and colour, typically giving the cumulate rock a layered or banded appearance.
Harzburgite, an ultramafic, igneous rock, is a variety of peridotite consisting mostly of the two minerals olivine and low-calcium (Ca) pyroxene (enstatite); it is named for occurrences in the Harz Mountains of Germany. It commonly contains a few percent chromium-rich spinel as an accessory mineral. Garnet-bearing harzburgite is much less common, found most commonly as xenoliths in kimberlite.
The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it fractionally crystallizes to become a felsic magma, which is low in magnesium and iron and produces rhyolite or granite. Calc-alkaline rocks are rich in alkaline earths and alkali metals and make up a major part of the crust of the continents.
The Stillwater igneous complex is a large layered mafic intrusion (LMI) located in southern Montana in Stillwater, Sweet Grass and Park Counties. The complex is exposed across 30 miles (48 km) of the north flank of the Beartooth Mountain Range. The complex has extensive reserves of chromium ore and has a history of being mined for chromium. More recent mining activity has produced palladium and other platinum group elements.
Enstatite chondrites are a rare form of meteorite, rich in the mineral enstatite. Only about 200 E-Type chondrites are currently known, comprising about 2% of the chondrites that fall on Earth. There are two main subtypes: EH and EL, classified based on their iron content.
Lizardite is a mineral from the serpentine subgroup with formula Mg3(Si2O5)(OH)4, and the most common type of mineral in the subgroup. It is also a member of the kaolinite-serpentine group.
