Tilasite is an

arsenate The arsenate ion is . An arsenate (compound) is any compound that contains this ion. Arsenates are salts or esters of arsenic acid. The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As(V). Arsenate resem ...

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. ( ...

gemstone A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...

, with the elemental formula Ca Mg( As O₄) F. It prefers 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 ...

form of crystal, and has Mohs hardness of 5. It was named in 1895 by

Hjalmar Sjögren Sten Anders Hjalmar Sjögren (13 June 1856, Färnebo, Värmland – 23 March 1922, Stockholm) was a Swedish geologist and mineralogist. Biography Sten Anders Hjalmar Sjögren became associate professor of mineralogy and geology at Uppsala Uni ...

in honor of

Daniel Tilas Daniel Tilas (11 March 1712 – 17 October 1772) was a Swedish mineralogist, mine expert, and an early pioneer of geology. The word feldspar was coined by Tilas although spelled as ''feldspat'' in the original. He was also among the early observers ...

, who was once director of mines for

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

, and a regional governor for

Västmanland Västmanland ( or ), is a historical Swedish province, or ''landskap'', in middle Sweden. It borders Södermanland, Närke, Värmland, Dalarna and Uppland. Västmanland means "(The) Land of the Western Men", where the "western men" (''västerm ...

. It was first discovered in Langban, Varmland. In 1972, Bladh et al. characterised samples found near Bisbee,

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

. In 1994, Bermanec discovered centro-symmetric Tilasite near Nezhilovo,

North Macedonia North Macedonia, ; sq, Maqedonia e Veriut, (Macedonia before February 2019), officially the Republic of North Macedonia,, is a country in Southeast Europe. It gained independence in 1991 as one of the successor states of Socialist Feder ...

.Bermanec V (1994) "Centro-symmetric tilasite from Nezilovo, Macedonia: a crystal structure refinement" Neues Jahrbuch für Mineralogie, Monatshefte 1994 289-294

References

Fluorine minerals Arsenic minerals Magnesium minerals {{halide-mineral-stub