Geikielite

Geikielite is a magnesium titanium oxide mineral with formula: MgTiO3. It is a member of the ilmenite group. It crystallizes in the trigonal system forming typically opaque, black to reddish black crystals.

Geikielite
Crystals of geikielite from the Maxwell quarry, Chelsea, Outaouais, Québec, Canada
General
CategoryOxide mineral
Formula
(repeating unit)
MgTiO3
Strunz classification4.CB.05
Crystal systemTrigonal
Crystal classRhombohedral (3)
(same H-M symbol)
Space groupR3
Unit cella = 5.05478(26) Å
c = 13.8992(7) Å; Z = 6
Identification
ColorBlack, ruby red uncommon; red internal reflections
Crystal habitTabular prismatic crystals, also as finely granular masses
CleavageGood on {1011}
Mohs scale hardness5 - 6
LusterSub-metallic
StreakPurplish brown
DiaphaneityOpaque to translucent
Specific gravity3.79 - 4.2
Optical propertiesUniaxial (-)
Refractive indexnω = 2.310 - 2.350 nε = 1.950 - 1.980
Birefringenceδ = 0.360 - 0.370
PleochroismWeak, O = pinkish red, E = brownish to purplish red
References[1][2][3]

It was first described in 1892[4] for an occurrence in the Ceylonese gem bearing gravel placers. It was named for Scottish geologist Sir Archibald Geikie (1835–1924).[3] It occurs in metamorphosed impure magnesian limestones, in serpentinite derived from ultramafic rocks, in kimberlites and carbonatites. Associated minerals include rutile, spinel, clinohumite, perovskite, diopside, serpentine, forsterite, brucite, hydrotalcite, chlorite and calcite.[1]

References

Further reading

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