Sapphirine is a rare

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

, a silicate of

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

and

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

( (with

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

as a major impurity). Named for its

sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sa ...

-like colour, sapphirine is primarily of interest to researchers and collectors: well-formed

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...

s are treasured and occasionally cut into gemstones. Sapphirine has also been synthesized for experimental purposes via a

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

process.

Properties

Typical colours range from light to dark sapphire blue, bluish to brownish green, green, and bluish or greenish gray to black; less common colours include yellow, pale red, and pink to purplish pink. Sapphirine is relatively hard (7.5 on

Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

), usually transparent to translucent, with a vitreous

lustre Lustre or Luster may refer to: Places * Luster, Norway, a municipality in Vestlandet, Norway ** Luster (village), a village in the municipality of Luster * Lustre, Montana, an unincorporated community in the United States Entertainment * '' ...

. Crystallising in the

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

system, sapphirine is typically anhedral or granular in

habit A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.

, but may also be tabular or in aggregates: Twinning is uncommon. Fracture is subconchoidal to uneven, and there is one direction of perfect cleavage. The

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

of sapphirine is 3.54–3.51, and its streak is white. Sapphirine's

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

(as measured by monochromatic

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

light, 589.3 nm) ranges from 1.701 to 1.718 with a birefringence of 0.006–0.007, biaxial negative. Refractive index values may correspond to colour: brownish green specimens will possess the highest values, purplish-pink specimens the lowest, and blue specimens will be intermediate between them.

Pleochroism Pleochroism (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Backgrou ...

may be extreme, with trichroic colours ranging from: colourless, pale yellow or red; sky to lavender blue, or bluish-green; to dark blue. There is no reaction under

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...

light.

Formation and occurrence

While there is evidence of magmatic origin in some deposits, sapphirine is primarily a product of high grade

metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ch ...

in environments poor in

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

and rich in magnesium and aluminium. However, sapphirine occurs in a variety of rocks, including

granulite Granulites are a class of high-grade metamorphic rocks of the granulite facies that have experienced high-temperature and moderate-pressure metamorphism. They are medium to coarse–grained and mainly composed of feldspars sometimes associated ...

and amphibolite facies, calc-silicate

skarn Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate mineral ...

s, and

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...

s; it is also known from

xenolith A xenolith ("foreign rock") is a rock fragment ( country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in ig ...

s. Associated minerals include: calcite,

chrysoberyl The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula Be Al2 O4. The name chrysoberyl is derived from the Greek words χρυσός ''chrysos'' and βήρυλλος ''beryllos'', meaning "a gold-white spar". Despite ...

cordierite Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: to . A high-temperat ...

, corundum,

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...

, kornerupine,

kyanite Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks gener ...

phlogopite Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. It is also known as magnesium mica. Phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula KMg3AlSi3O ...

scapolite The scapolites (Gr. σκάπος, rod, and λίθος, stone) 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 marialit ...

sillimanite Sillimanite is an aluminosilicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman (1779–1864). It was first described in 1824 for an occurrence in Chester, Connecticut. Occurrence ...

, spinel, and surinamite. Large crystals of fine clarity and colour are known from very few locales: The Central Province ( Hakurutale and Munwatte) of Sri Lanka has long been known as a source of facetable greenish blue to dark blue material, and crystals up to 30 mm or more in size have been found in Fianarantsoa (

Betroka District Betroka is a district of Anosy in Madagascar. Communes The district is further divided into 20 communes: * Ambalasoa * Ambatomivary * Analamary * Andriandampy * Beapombo I * Beapombo II * Bekorobo * Benato-Toby * Betroka * Iaborotra * ...

) and

Toliara Province The Toliara Province (formerly Toliary or Tuléar) is a former province of Madagascar with an area of . It had a population of 2,229,550 (July, 2001). Its capital was Toliara. Near Toliara was the " spiny forest". Toliara Province bordered the fol ...

(Androy and Anosy regions), southern Madagascar. Sapphirine's type locality is Fiskenaesset (Fiskenaes),

Nuuk Nuuk (; da, Nuuk, formerly ) is the capital and largest city of Greenland, a constituent country of the Kingdom of Denmark. Nuuk is the seat of government and the country's largest cultural and economic centre. The major cities from other coun ...

region, western Greenland, which is where the mineral was discovered in 1819. Other notable localities include: Western Hoggar,

Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig ...

; the Napier complex of

Enderby Land Enderby Land is a projecting landmass of Antarctica. Its shore extends from Shinnan Glacier at about to William Scoresby Bay at , approximately of the earth's longitude. It was first documented in western and eastern literature in February 18 ...

and the

Vestfold Hills The Vestfold Hills are rounded, rocky, coastal hills, in extent, on the north side of Sorsdal Glacier on the Ingrid Christensen Coast of Princess Elizabeth Land, Antarctica. The hills are subdivided by three west-trending peninsulas bounded by n ...

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

; Delegate, New South Wales and the Strangways Range of the

Northern Territory The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an Australian territory in the central and central northern regions of Australia. The Northern Territory shares its borders with Western Aust ...

, Australia; Wilson Lake,

Labrador , nickname = "The Big Land" , etymology = , subdivision_type = Country , subdivision_name = Canada , subdivision_type1 = Province , subdivision_name1 ...

; Donghai,

Jiangsu Jiangsu (; ; pinyin: Jiāngsū, alternatively romanized as Kiangsu or Chiangsu) is an eastern coastal province of the People's Republic of China. It is one of the leading provinces in finance, education, technology, and tourism, with its ca ...

province, China;

Kittilä Kittilä ( se, Gihttel, smn, Kittâl, sms, Kihttel) is a municipality of Finland and a popular holiday resort. It is located in northern Finland north of the Arctic Circle within the Lapland region. The municipality has a population of () and ...

, Lapland, Finland; Ariège,

Midi-Pyrénées Midi-Pyrénées (; oc, Miègjorn-Pirenèus or ; es, Mediodía-Pirineos) is a former administrative region of France. Since 1 January 2016, it has been part of the new region of Occitania. It was the largest region of Metropolitan France by ar ...

, France; Waldheim, Saxony, Germany; Dora Maira Massif,

Province of Cuneo Cuneo (Italian), or Coni (Piedmontese), is a province in the southwest of the Piedmont region of Italy. To the west it borders on the French region of Provence-Alpes-Côte d'Azur ( departments of Alpes-Maritimes, Alpes-de-Haute-Provence and Haut ...

, Piedmont, Italy;

Ulstein Ulstein is a municipality in Møre og Romsdal county, Norway. It is part of the Sunnmøre region. The commercial and administrative centre of Ulstein is the town of Ulsteinvik. The municipality occupies the western half of the island of Hareid ...

, Møre og Romsdal, and

Meløy Meløy is a municipality in Nordland county, Norway. It is part of the Salten traditional region. The administrative centre of the municipality is the village of Ørnes. Other villages include Eidbukta, Neverdal, Glomfjord, Halsa, Reipå, S ...

, Nordland, Norway; the Messina District of

Limpopo Province Limpopo is the northernmost province of South Africa. It is named after the Limpopo River, which forms the province's western and northern borders. The capital and largest city in the province is Polokwane, while the provincial legislature is ...

and the Okiep Copper District of

Northern Cape Province The Northern Cape is the largest and most sparsely populated province of South Africa. It was created in 1994 when the Cape Province was split up. Its capital is Kimberley. It includes the Kalahari Gemsbok National Park, part of the Kgalagadi ...

, South Africa;

Falkenberg Municipality Falkenberg Municipality (''Falkenbergs kommun'') is a municipality in Halland County on the Swedish west coast. The town Falkenberg is the municipal seat. The municipality was created in 1971 when the ''City of Falkenberg'' was amalgamated with ...

, Halland County, Sweden; Mautia Hill in the Kongwa region of Central Province, Tanzania;

Isle of Harris Harris ( gd, Na Hearadh, ) is the southern and more mountainous part of Lewis and Harris, the largest island in the Outer Hebrides, Scotland. Although not an island itself, Harris is often referred to in opposition to the ''Isle of Lewis'' as t ...

, Outer Hebrides, Scotland; the Bani Hamid area of

Semail Ophiolite The Samail Ophiolite (also spelled Semail Ophiolite) of the Hajar Mountains of Oman and the United Arab Emirates is a large slab of oceanic crust, made of volcanic rocks and ultramafic rocks from the Earth's upper mantle, that was overthrust ont ...

, United Arab Emirates; the

Dome Rock Mountains The Dome Rock Mountains are a mountain range in southern La Paz County, Arizona. The range borders the Colorado River on the west and the Colorado River Indian Reservation on the northwest located in the Lower Colorado River Valley. Quartzsite, ...

of La Paz County, Arizona, Stockdale,

Riley County, Kansas Riley County (standard abbreviation: RL) is a county located in the U.S. state of Kansas. As of the 2020 census, the population was 71,959. The largest city and county seat is Manhattan. Riley County is home to two of Kansas's largest employer ...

;

Cortlandt, New York Cortlandt is a town in Westchester County, New York, United States, located at the northwestern edge of the county, at the eastern terminus of the Bear Mountain Bridge. The town includes the villages of Buchanan and Croton-on-Hudson. History T ...

; and

Clay County, North Carolina Clay County is a county located in the far western part of U.S. state North Carolina. As of the 2020 census, the county population was 11,089. The county seat is Hayesville, elevation 1,893 ft. History This area was occupied by the Cherokee ...

; India The Eastern Ghats Mobile Belt. Sapphirine was also reported as a reaction product (together with garnet) in between Mg-Al-spinel and Ca-Tschermak-rich clinopyroxene in corundum-bearing mantle pyroxenites. Kornprobst J., Piboule M., Roden M. & Tabit A.- 1990. Corundum-bearing garnet clinopyroxenites at Beni Bousera (Morocco): original plagioclase-rich gabbros recrystallized at depth within the mantle ? J. Petrology, 31, 3, 717-745

References

{{Commons category Magnesium minerals Aluminium minerals Inosilicates Gemstones Triclinic minerals Minerals in space group 2 Minerals in space group 10