Schreyerite

Schreyerite
General
Category Oxide mineral
Formula
(repeating unit)		 V2Ti3O9
Strunz classification 4.CB.35
Crystal system Monoclinic
Crystal class Prismatic (2/m)
H-M symbol: (2/m)
Space group C2/c
Unit cell a = 7.06 Å, b = 5.01 Å
c = 18.74 Å; β = 119.4°; Z = 4
Identification
Color Reddish brown; gray in reflected light
Crystal habit As lamellae and microscopic grains, exsolved within rutile crystals
Twinning Polysynthetic, universal
Mohs scale hardness 7
Luster Metallic
Diaphaneity Opaque
Optical properties Biaxial
Refractive index n = 2.700
Pleochroism Weak; yellow-brown to reddish brown
References [1][2][3]

Schreyerite (V2Ti3O9), is a vanadium, titanium oxide mineral found in the Lasamba Hill, Kwale district in Coast Province Kenya. It is polymorphous with kyzylkumite.

The mineral occurs as exsolution lamellae and particles in rutile, coexisting with kyanite, sillimanite, and tourmaline in a highly metamorphosed gneiss. It was named after German mineralogist and petrologist Werner Schreyer, for his research on mineralogy of rock-forming minerals and petrology of metamorphic rocks both in nature and by experiment.

Introduction

Investigation of deposits of green vanadium-bearing kornerupine, revealed the presence of a new vanadium mineral through observations in reflected light. Schreyerite was first discovered in the Kwale district, Kenya. Polymorphous with kyzylkumite, it occurs in highly twinned unmixed grains in vanadium-bearing rutile that occurs as idiomorphic crystals in kornerupine-bearing quartz-biotite-sillimanite gneiss. It also occurs in a pyrite deposit at Sartra, Sweden, in a Pb-Zn ore deposit at Rampura Agucha, India, and recently in metamorphic rocks of the Ol’khon complex on the western shore of Lake Baikal, Russia. Instead of the usual intergrowths with rutile, single crystals of schreyerite were found, associated with titanite.

Optical and physical properties

Schreyerite is a reddish-brown, opaque mineral with metallic luster. Its reflectivity is slightly lower than rutile, and as a result, it is mostly gray. Pleochromism is weak: yellowish brown to reddish brown. When immersed in oil, the contrasts between rutile and schreyerite become clearer, and the color becomes more intense.

With crossed polarizers, moderate anisotropism becomes evident, so that the very fine lamellar twinning becomes distinct. It has hardness of 7 and calculated specific gravity of 4.46.

References

  1. ↑ Mindat.org
  2. ↑ Webmineral.com
  3. ↑ Handbook of Mineralogy
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