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.
In 1972, Bladh et al. characterised samples found near Bisbee, Arizona.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
In 1994, Bermanec discovered centro-symmetric Tilasite near Nezhilovo, North Macedonia.Bermanec V (1994) "Centro-symmetric tilasite from Nezilovo, Macedonia: a crystal structure refinement" Neues Jahrbuch für Mineralogie, Monatshefte 1994 289-294
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