Vuagnatite

Vuagnatite is a member of the adelite-descloizite group which was named after Prof. Dr. Marc Bernard Vuagnat. Its type locality is in Turkey, at Bögürtlencik Tepe. It was approved in 1975 by the IMA.[2]

Vuagnatite
General
CategoryMineral
Formula
(repeating unit)
CaAl(SiO4)(OH)
IMA symbolVgn[1]
Strunz classification9.AG.60
Dana classification52.4.2.2
Crystal systemOrthorhombic
Crystal classDisphenoidal
[[H-M Symbol]]: 222
Space groupP212121
Unit cell341.98
Identification
ColorColourless, light blue, light pink, tan
CleavagePerfect
TenacityBrittle
Mohs scale hardness6
LusterVitreous
StreakWhite
DiaphaneityTransparent, translucent
Optical propertiesBiaxial (-)
Refractive indexnα = 1.700
nβ = 1.725
nγ = 1.730
Birefringence0.030
2V angleMeasured: 48°
Calculated: 46°
DispersionRelatively weak
Common impuritiesH2O

Properties

Vuagnatite is a mineral mainly consisting of oxygen (45.41%), calcium (22.75%), silicon (15.94%) and aluminum (15.32%), with traces of hydrogen (0.57%). It does not show radioactive properties.[3] It widely occurs in prehnite and in hydrogrossular assemblages. It was first reported from an ophiolite suite in rodingite dikes. It has been described from rodingitised gabbro, rodingites and greywacke cobbles, and as veins in serpentinite. Some of the recorded occurrences were in Japan, New Zealand, Turkey, Guatemala and California. It grows in small, inclusion-free, chemically pure isometric crystals up to a millimeter. The brown coloration is most probably caused by the high quantity of iron oxide within the mineral, as darker specimens are rich in both titanium dioxide and iron oxide. Some of the crystals have small zones which seems to be continuous with the rest of the crystal, that shows deeper coloring. Some of the samples of these properties have either a brown or blueish coloring, but other colors are not out of the question. It shows pleochroic attributes, meaning depending on which axis the mineral is seen on, it appears as if it is changing colors. On the α axis it is seen in a pale brown, almost pinkish color, but on the β and γ ones, it appears to be colourless.[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. "Vuagnatite". www.mindat.org. Retrieved 2021-10-04.
  3. "Vuagnatite Mineral Data". www.webmineral.com. Retrieved 2021-10-04.
  4. Craw, David; Landis, Charles A.; Kawachi, Yosuke (October 1979). "Vuagnatite in New Zealand (Note)". New Zealand Journal of Geology and Geophysics. 22 (5): 627–629. doi:10.1080/00288306.1979.10424172. ISSN 0028-8306.
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