Tilasite

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]

Grischunite and Tilasite: Well formed orange brown grischunite crystals associated to almost white tilasite crystals. From: Falotta, Tinzen, Grischun, Switzerland
General
CategoryMineral
Formula
(repeating unit)
CaMg(AsO4)F
IMA symbolTil[1]
Strunz classification8.BH.10
Dana classification41.5.6.1
Crystal systemMonoclinic
Unit cella = 6.681 Å, b = 8.950 Å, c = 7.573 Å β = 121.14°
Structure
Identification
Formula mass222.30
Mohs scale hardness5
DiaphaneityTranslucent
Specific gravity3.75 - 3.79
Optical propertiesBiaxial (-)
Refractive indexnα = 1.640 nβ = 1.660 nγ = 1.675
Birefringence0.035
2V angle83°
Dispersionrelatively weak

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

  1. 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.
  2. "Tilasite".
  3. 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
  4. 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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