232 articles
Biotite
Biotite, also known as black mica, is the group name for dark, iron-rich mica minerals occurring widely in igneous and metamorphic rocks such as granite and gneiss.
Birnessite
Birnessite is a hydrous layered manganese oxide mineral, first described in 1956 from Birness, Aberdeenshire, Scotland, and common in soils, desert varnish, and marine manganese nodules.
Birthstone
A birthstone is a gemstone assigned to a person's month of birth, worn as jewelry or given as a gift; the modern American list was standardized in 1912.
Bornite
Bornite is a copper iron sulfide mineral, Cu5FeS4, and an important ore of copper, best known for the iridescent blue and purple tarnish called "peacock ore."
Bridgmanite
Bridgmanite is magnesium silicate perovskite, (Mg,Fe)SiO3, the most abundant mineral on Earth, dominating its lower mantle. It was named in 2014 for physicist Percy Bridgman.
Brownmillerite
Brownmillerite is a reddish-brown calcium iron aluminate oxide mineral with the ideal formula Ca₂Fe³⁺AlO₅, occurring in thermally metamorphosed limestones in Israel and Germany and forming the ferrite phase of Portland cement clinker.
Brucite
Brucite is a magnesium hydroxide mineral, Mg(OH)₂, described in 1824 from New Jersey serpentine and named for Archibald Bruce; it reacts readily with CO₂ for mineral carbonation.
Burmese amber
Burmese amber, also known as burmite, Kachin amber, or Myanmar amber, is fossil tree resin from the Hukawng Valley of northern Myanmar, about 99 million years old.
Cabochon
A cabochon, also called en cabochon, is a gemstone polished into a smooth dome rather than cut with facets, often chosen for opaque or translucent stones.
Calcite
Calcite, also known as calcareous spar, is a common calcium carbonate mineral crystallizing in the trigonal system; it forms limestone and marble, and clear Iceland spar shows strong double refraction.
Carbonado
Carbonado, also known as black diamond, is an opaque black natural polycrystalline diamond found only in Brazil and the Central African Republic, with no known source rock.
Carbonate minerals
Carbonate minerals are minerals containing the carbonate ion CO3, combined with metals such as calcium and magnesium; calcite and dolomite make up over 90 percent of them.
Carnelian
Carnelian, also called Corniola, is a translucent red to reddish-orange variety of chalcedony, a microcrystalline quartz colored by iron oxide, prized since antiquity for seals and beads.
Cassiterite
Cassiterite is a dense, hard tin oxide mineral, SnO₂, and the principal ore of tin, found in granite-related veins and in placer deposits formed as they weather.
Caswellsilverite
Caswellsilverite is a rare sodium chromium sulfide mineral with the formula NaCrS₂, approved by the International Mineralogical Association in 1981 and known almost entirely from enstatite-rich meteorites, first described from the Norton County meteorite in Kansas.
Cerussite
Cerussite is a lead carbonate mineral (PbCO₃) that forms as a secondary mineral in the oxidized zone of lead deposits, where it is an important lead ore.
Chalcedony
Chalcedony is a microcrystalline form of silica, SiO2, made of quartz crystals too small to resolve under an ordinary microscope, and the umbrella term for varieties including agate, jasper, and carnelian.
Chalcocite
Chalcocite is a dark lead-gray copper sulfide mineral, Cu₂S, and an important copper ore with about 79.8 percent copper by weight, found mainly in supergene zones of copper deposits.
Chalcopyrite
Chalcopyrite, also known as copper pyrites, is a brass-yellow copper iron sulfide mineral that is the world's most abundant copper source and the main mineral in porphyry deposits.
Chamosite
Chamosite is a green iron-rich mineral of the chlorite group and the iron analog of clinochlore, named in 1820 for Chamoson, Switzerland, and best known as a main constituent of oolitic ironstones, sedimentary iron ores.
Changesite-(Y)
Changesite-(Y) is a phosphate mineral of the merrillite group, found in lunar soil returned by China's Chang'e 5 mission and approved as a new mineral species in 2022.
Chromite
Chromite, sold industrially as chrome ore, is an iron chromium oxide mineral of the spinel group and the only commercial source of chromium, smelted mostly into ferrochrome for stainless steel.
Chrysoberyl
Chrysoberyl is a rare beryllium aluminum oxide mineral, BeAl₂O₄, prized as a gemstone and best known for its alexandrite variety, which changes color, and its chatoyant cat's-eye.
Chrysotile
Chrysotile, also called white asbestos, is a fibrous serpentine mineral and the most widely used asbestos in commerce, found in cement, brakes, and insulation until banned by the EPA in 2024.
Cinnabar
Cinnabar is a bright red mercury sulfide mineral, HgS, the chief ore from which mercury is extracted by roasting and the source of the pigment vermilion.
Citrine
Citrine, from the French citron meaning lemon, is the transparent yellow to brownish orange gem variety of quartz colored by trace iron, and a November birthstone with topaz.
Cleavage (crystal)
Cleavage, or mineral cleavage, is the tendency of a crystal to break along flat planes where atomic bonds are weakest, a key property for identifying minerals.
Clinoenstatite
Clinoenstatite is a monoclinic pyroxene mineral with the ideal formula Mg₂Si₂O₆, the low-temperature polymorph of enstatite, known from the Bonin Islands and used as a shock indicator in meteorites.
Clinoptilolite
Clinoptilolite is a naturally occurring microporous aluminosilicate zeolite of the heulandite group, the most abundant natural zeolite, valued for ion exchange and adsorption in pet litter, animal feed, and wastewater treatment.
Clinozoisite
Clinozoisite is a calcium aluminum sorosilicate mineral, Ca₂Al₃(Si₂O₇)(SiO₄)O(OH), belonging to the epidote group; it is the monoclinic dimorph of zoisite and forms a solid-solution series with epidote.