232 articles
Flint
Flint is a hard, dark sedimentary rock made of microcrystalline quartz, occurring as nodules in chalk, whose conchoidal fracture gives razor-sharp edges prized for prehistoric tools and fire starting.
Fluorapatite
Fluorapatite is a calcium fluoride phosphate mineral, Ca5(PO4)3F, and the most abundant member of the apatite group, forming the sedimentary phosphorite deposits that supply the world's phosphorus fertilizer.
Fulgurite
A fulgurite, popularly called petrified lightning, is a natural glass tube or crust formed when a lightning strike melts and fuses sand, soil, or rock.
Fuller's earth
Fuller's earth, also known as bleaching earth or Multani Mitti, is any naturally occurring clay with high absorptive capacity, used to clean wool, absorb oils, and decolorize fats.
Galena
Galena, also known as lead glance or blue lead, is lead sulfide, the world's most important ore of lead, used by humans for thousands of years.
Garnet
Garnet is a group of silicate minerals that supplies gemstones in nearly every color and a hard abrasive for waterjet cutting; it is January's birthstone.
Gemstone
A gemstone, also called a precious or semiprecious stone, is a mineral or organic material cut and polished for jewelry and valued for beauty, durability, and rarity.
Geode
A geode is a roughly spherical rock with a hollow interior cavity lined with mineral crystals, formed when dissolved minerals precipitate in volcanic or sedimentary rock.
Gibbsite
Gibbsite, also known as hydrargillite, is an aluminum hydroxide mineral, Al(OH)₃, and one of the three principal minerals of bauxite, the ore from which nearly all aluminum is produced.
Glauconite
Glauconite is a green iron- and potassium-rich clay mineral of the mica group, named in 1828 from the Greek glaucos for bluish green; sand rich in it is called greensand.
Golden Jubilee Diamond
The Golden Jubilee Diamond, also called the Golden Jubilee, is the world's largest faceted diamond, a 545.67-carat yellow-brown gem presented to King Bhumibol Adulyadej of Thailand.
Grossular
Grossular is a calcium aluminum silicate mineral of the garnet group, the most varicolored of the six common garnets, including gem varieties hessonite and tsavorite.
Hashemite (mineral)
Hashemite is a rare barium chromate mineral, Ba(Cr,S)O₄, isostructural with baryte, first described in 1983 from west-central Jordan and named for the Hashemite Kingdom of Jordan.
Heliotrope (mineral)
Heliotrope, also called bloodstone, is a dark green variety of chalcedony spotted with red iron-oxide markings resembling drops of blood, long used for seals and signet rings.
Hematite
Hematite is an iron oxide mineral, Fe₂O₃, and the most important ore of iron; most formed in Precambrian banded iron formations, and it also occurs on Mars.
Herkimer diamond
The Herkimer diamond, also called Little Falls Diamond, is a doubly terminated quartz crystal found in Herkimer County, New York; it is quartz, not true diamond.
Heterogenite
Heterogenite is a cobalt oxyhydroxide mineral, CoO(OH), the most abundant oxidized cobalt mineral and principal cobalt ore in the Katanga Copperbelt of the Democratic Republic of Congo.
Hope Diamond
The Hope Diamond, or Le Bijou du Roi, is a 45.52-carat deep grayish-blue diamond cut from the stolen French Blue and displayed at the Smithsonian since 1958.
Hornblende
Hornblende is a root-name group of dark green to black calcic amphibole minerals, documented by Abraham Gottlieb Werner in 1789, found in rocks such as granite, diorite, gabbro, and schist.
Hydroxyapatite
Hydroxyapatite, also known as calcium hydroxyapatite or hydroxylapatite, is a calcium phosphate mineral with formula Ca10(PO4)6(OH)2 that forms most of human bone and tooth enamel.
Imogolite
Imogolite is a poorly crystalline hydrous aluminosilicate clay mineral, first described in 1962 from volcanic ash soils in Japan, whose hollow nanotubes occur in volcanic ash soils worldwide.
Iron peroxide
Iron peroxide is a pyrite-structured iron oxide, FeO2, reported in 2016, which forms under deep lower-mantle pressures when the mineral goethite decomposes and is a candidate for ultralow-velocity zones above Earth's core.
Jacobsite
Jacobsite is a black, weakly magnetic manganese iron oxide mineral of the spinel group, occurring in metamorphosed manganese deposits and named in 1869 for Jakobsberg, Sweden.
Jacutingaite
Jacutingaite (Pt₂HgSe₃) is a naturally occurring layered platinum-group mineral discovered in Brazil in 2008, whose exfoliated monolayer is a large-gap quantum spin Hall insulator realizing the Kane–Mele model.
Jade
Jade is a name shared by two distinct, exceptionally tough gem materials, nephrite and jadeite, whose finest form, imperial jadeite from northern Myanmar, is translucent emerald green.
Jadeite
Jadeite, known in Chinese as fei cui (翡翠), is a sodium aluminum pyroxene mineral and the more prized of the two minerals called jade, valued for its imperial-green variety.
Jasper
Jasper is an opaque, impure variety of cryptocrystalline silica, typically red to reddish-brown from hematite inclusions; the name comes from ancient Greek for "spotted stone," and it has been used since prehistory.
Kaolin
Kaolin, also called china clay, is a soft white clay consisting mainly of kaolinite, named after Gaoling in China and consumed chiefly by the paper and ceramics industries.
Kaolinite
Kaolinite, the principal mineral of kaolin or china clay, is a white layered clay mineral named after Gaoling, China, and used in porcelain, paper, and ceramics.
Kassite
Kassite is a rare calcium titanium oxide mineral named in 1965 for geologist Nikolai Kassin, first found at the Afrikanda complex on the Kola Peninsula, Russia.