Lepidolite is the common name for a

lilac ''Syringa'' is a genus of 12 currently recognized species of flowering woody plants in the olive family or Oleaceae called lilacs. These lilacs are native to woodland and scrub from southeastern Europe to eastern Asia, and widely and commonly ...

-gray or rose-colored series of minerals in the

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

group. The mineralogical name for this series is the polylithionite-trilithionite series. Lepidolite has a chemical formula of . It is the most abundant

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

-bearing mineral and is a secondary source of this metal. It is the major source of the

alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

rubidium Rubidium is a chemical element; it has Symbol (chemistry), symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have ...

. Lepidolite is found with other lithium-bearing minerals, such as

spodumene Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, Li Al( Si O3)2, and is a commercially important source of lithium. It occurs as colorless to yellowish, purplish, or lilac kunzite (see below), or alternatively yellow ...

, in

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic c ...

bodies. It has also been found in high-temperature quartz veins, greisens and granite.

Description

Lepidolite is a

phyllosilicate 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 ...

mineral and a member of the polylithionite-trilithionite series. Lepidolite is part of a three-part series consisting of polylithionite, lepidolite, and trilithionite. All three minerals share similar properties and are caused because of varying ratios of lithium and aluminum in their chemical formulas. The Li:Al ratio varies from 2:1 in polylithionite up to 1.5:1.5 in trilithionite. Lepidolite is found naturally in a variety of colors, mainly pink, purple, and red, but also gray and, rarely, yellow and colorless. Because lepidolite is a lithium-bearing mica, it is often wrongly assumed that lithium is what causes the pink hues that are so characteristic of this mineral. Instead, it is trace amounts of manganese that cause the pink, purple, and red colors.

Structure and composition

Lepidolite belongs to the group of trioctahedral micas, with a structure resembling

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...

. This structure is sometimes described as ''TOT-c''. The crystal consists of stacked ''TOT'' layers weakly bound together by potassium ions (''c''). Each ''TOT'' layer consists of two outer ''T'' (tetrahedral) sheets in which silicon or aluminium ions each bind with four oxygen atoms, which in turn bind to other aluminium and silicon to form the sheet structure. The inner ''O'' (octahedral) sheet contains iron or magnesium ions each bonded to six oxygen, fluoride, or hydroxide ions. In biotite, silicon occupies three out of every four tetrahedal sites in the crystal and aluminium occupies the remaining tetrahedral sites, while magnesium or iron fill all the available octahedral sites. Lepidolite shares this structure, but aluminium and lithium substitute for magnesium and iron in the octahedral sites. If nearly equal quantities of aluminium and lithium occupy the octahedral sites, the resulting mineral is trilithionite, If lithium occupies two out of three octahedral sites and aluminium the remaining octahedra site, then charge balance can be preserved only if silicon occupies all the tetrahedral sites. The result is polylithionite, . Lepidolite has a composition intermediate between these end members. Fluoride ions can substitute for some of the hydroxide in the structure, while

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

, or

caesium Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has Symbol (chemistry), symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only f ...

may substitute in small quantities for potassium.

Occurrences

Lepidolite is associated with other lithium-bearing minerals like

bodies. It is the major source of the

. In 1861,

Robert Bunsen Robert Wilhelm Eberhard Bunsen (; 30 March 1811 – 16 August 1899) was a German chemist. He investigated emission spectra of heated elements, and discovered caesium (in 1860) and rubidium (in 1861) with the physicist Gustav Kirchhoff. The Bu ...

and

Gustav Kirchhoff Gustav Robert Kirchhoff (; 12 March 1824 – 17 October 1887) was a German chemist, mathematician, physicist, and spectroscopist who contributed to the fundamental understanding of electrical circuits, spectroscopy and the emission of black-body ...

extracted of lepidolite to yield a few grams of rubidium salts for analysis, and therefore discovered the new element rubidium. It occurs in

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

s, in some high-temperature quartz veins, greisens and granites. Associated minerals include

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

feldspar Feldspar ( ; sometimes spelled felspar) 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 ''plagiocl ...

amblygonite Amblygonite () is a fluorophosphate mineral, , composed of lithium, sodium, aluminium, phosphate, fluoride and hydroxide. The mineral occurs in pegmatite deposits and is easily mistaken for albite and other feldspars. Its density, cleavage and fl ...

tourmaline Tourmaline ( ) is a crystalline silicate mineral, silicate mineral group in which boron is chemical compound, compounded with chemical element, elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a ...

columbite Columbite, also called niobite, niobite-tantalite and columbate, with a general chemical formula of , is a black mineral group that is an ore of niobium. It has a submetallic luster, a high density, and is a niobate of iron and manganese. Niobite ...

cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains ...

topaz Topaz is a silicate mineral made of aluminium, aluminum and fluorine with the chemical formula aluminium, Alsilicon, Sioxygen, O(fluorine, F, hydroxide, OH). It is used as a gemstone in jewelry and other adornments. Common topaz in its natural ...

and

beryl Beryl ( ) is a mineral composed of beryllium aluminium Silicate minerals#Cyclosilicates, silicate with the chemical formula Be3Al2(SiO3)6. Well-known varieties of beryl include emerald and Aquamarine (gem), aquamarine. Naturally occurring Hex ...

. Notable occurrences include

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 ...

;

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;

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 the

Black Hills The Black Hills is an isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, United States. Black Elk Peak, which rises to , is the range's highest summit. The name of the range ...

, United States;

Tanco Mine The Tanco Mine or Bernic Lake mine is an underground caesium and tantalum mine, owned and since 2019 owned and operated by Sinomine Resource Group on the north west shore of Bernic Lake, Manitoba, Canada. The mine has the largest known deposit ...

Bernic Lake Bernic Lake is a lake in the eastern part of the province of Manitoba, Canada. It is located just southwest of Nopiming Provincial Park, and just north of Whiteshell Provincial Park. The Tanco mine is located on the northwestern shore of the ri ...

Manitoba Manitoba is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population ...

, Canada; and

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

. File:Lepidolite-140533.jpg, Yellow lepidolite from Itinga,

Minas Gerais Minas Gerais () is one of the 27 federative units of Brazil, being the fourth largest state by area and the second largest in number of inhabitants with a population of 20,539,989 according to the 2022 Brazilian census, 2022 census. Located in ...

, Brazil. Size: 6.1 x 4.9 x 3.1 cm File:Lepidolite-208658.jpg, Lavender lepidolite "books" from Himalaya Mine, Mesa Grande District,

San Diego County, California San Diego County (), officially the County of San Diego, is a county (United States), county in the southwest corner of the U.S. state of California, north to its Mexico-United States border, border with Mexico. As of the 2020 United States Cen ...

, US. Size: 4.8 x 3.9 x 3.5 cm File:Lepidolite-76774.jpg, Lepidolite, Virgem da Lapa,

, Brazil (size 2.4 x 2.1 x 0.7 cm) File:Radiating lepidolite White Elephant Mine SD.jpg, Radiating lepidolite at the White Elephant pegmatite, Black Hills, South Dakota

References

{{Authority control Phyllosilicates Lithium minerals Potassium minerals Aluminium minerals Monoclinic minerals Minerals in space group 8 Minerals in space group 12 Mica group Luminescent minerals Gemstones Rubidium compounds