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.
Feldspar is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust, and 41% of the Earth's continental crust by weight.
Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks.
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.
Sekaninaite ((Fe+2,Mg)2Al4Si5O18) is a silicate mineral, the iron-rich analogue of cordierite.
Augite, also known as Augurite, is a common rock-forming pyroxene mineral with formula (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees.
Wollastonite is a calcium inosilicate mineral (CaSiO3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure limestone or dolomite is subjected to high temperature and pressure, which sometimes occurs in the presence of silica-bearing fluids as in skarns or in contact with metamorphic rocks. Associated minerals include garnets, vesuvianite, diopside, tremolite, epidote, plagioclase feldspar, pyroxene and calcite. It is named after the English chemist and mineralogist William Hyde Wollaston (1766–1828).
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).
The scapolites are a group of rock-forming silicate minerals composed of aluminium, calcium, and sodium silicate with chlorine, carbonate and sulfate. The two endmembers are meionite and marialite. Silvialite (Ca,Na)4Al6Si6O24(SO4,CO3) is also a recognized member of the group.
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).
Diallage is an inosilicate, meaning it is 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.
Hedenbergite, CaFeSi2O6, is the iron rich end member of the pyroxene group having a monoclinic crystal system. The mineral is extremely rarely found as a pure substance, and usually has to be synthesized in a lab. It was named in 1819 after M.A. Ludwig Hedenberg, who was the first to define hedenbergite as a mineral. Contact metamorphic rocks high in iron are the primary geologic setting for hedenbergite. This mineral is unique because it can be found in chondrites and skarns (calc–silicate metamorphic rocks). Since it is a member of the pyroxene family, there is a great deal of interest in its importance to general geologic processes.
Melilite refers to a mineral of the melilite group. Minerals of the group are solid solutions of several endmembers, the most important of which are gehlenite and åkermanite. A generalized formula for common melilite is (Ca,Na)2(Al,Mg,Fe2+)[(Al,Si)SiO7]. Discovered in 1793 near Rome, it has a yellowish, greenish-brown color. The name derives from the Greek words meli (μέλι) "honey" and lithos (λίθους) "stone".The name refers to a group of minerals (melilite group) with chemically similar composition, nearly always minerals in åkermanite-gehlenite series.
Mineral alteration refers to the various natural processes that alter a mineral's chemical composition or crystallography.
Davisite is an exceedingly rare mineral of the pyroxene group, with formula CaScAlSiO6. It is the scandium-dominant member. It stands for scandium-analogue of other pyroxene-group members, esseneite, grossmanite and kushiroite. Davisite is one of scarce minerals containing essential scandium.
Grossmanite is a very rare mineral of the pyroxene group, with formula CaTi3+AlSiO6. It is the titanium-dominant member. Grossmanite is unique in being a mineral with trivalent titanium, a feature shared with tistarite, Ti2O3. Titanium in minerals is almost exclusively tetravalent. Grossmanite stands for titanium-analogue of davisite, esseneite and kushiroite – other members of the pyroxene group. Both grossmanite and tistarite come from the famous Allende meteorite.
Kushiroite is a rare mineral of the pyroxene group, with formula CaAlAlSiO6. It is the fully aluminian member. The formula of kushiroite corresponds to the molecule (or component) known as Calcium-Tschermak (Ca-Tschermak), which dominates in the composition of kushiroite. Kushiroite is an aluminium-analogue of other pyroxene-group members, davisite, esseneite, and grossmanite. It was found in a chondrite meteorite within refractory inclusions.
Eric J. Essene was a professor emeritus of geosciences and a metamorphic petrologist at the University of Michigan. In 2010, Essene was awarded the Penrose Medal by the Geological Society of America. He was a leader in the development of geothermobarometry as a tool in understanding the rock assemblages of high grade metamorphic suites and the evolution of continental crust.
