Tilasite
(repeating unit)CaMg(AsO4)F IMA symbol Til[1] Strunz classification 8.BH.10 Dana classification 41.5.6.1 Crystal system Monoclinic Unit cell a = 6.681 Å, b = 8.950 Å, c = 7.573 Å β = 121.14° Structure Identification Formula mass 222.30 Mohs scale hardness 5 Diaphaneity Translucent Specific gravity 3.75 - 3.79 Optical properties Biaxial (-) Refractive index nα = 1.640 nβ = 1.660 nγ = 1.675 Birefringence 0.035 2V angle 83° Dispersion relatively weak
Tilasite is an arsenate mineral gemstone, with the elemental formula CaMg(AsO4)F. It prefers the monoclinic form of crystal, and has Mohs hardness of 5. It was named in 1895 by Hjalmar Sjögren in honor of Daniel Tilas, who was once director of mines for Sweden, and a regional governor for Västmanland. It was first discovered in Langban, Varmland.[2]
In 1972, Bladh et al. characterised samples found near Bisbee, Arizona.[3]
In 1994, Bermanec discovered centro-symmetric Tilasite near Nezhilovo, North Macedonia.[4]
References
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ "Tilasite".
- ^ Bladh K W, Corbett R K, McLean W J, Laughon R B. American Mineralogist 57 (1972) 1880-1884 "The crystal structure of tilasite" http://rruff.geo.arizona.edu/AMS/minerals/Tilasite
- ^ Bermanec V (1994) "Centro-symmetric tilasite from Nezilovo, Macedonia: a crystal structure refinement" Neues Jahrbuch fur Mineralogie, Monatshefte 1994 289-294
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