Geikielite

Magnesium titanium oxide mineral

Geikielite

Crystals of geikielite from the Maxwell quarry, Chelsea, Outaouais, Québec, Canada

General Category

Oxide mineral

Formula
(repeating unit)

MgTiO3

IMA symbol

Gk

Strunz classification

4.CB.05

Crystal system

Trigonal

Crystal class

Rhombohedral (3)
(same H-M symbol)

Space group

R3

Unit cell

a = 5.05478(26) Å
c = 13.8992(7) Å; Z = 6

Identification Color

Black, ruby red uncommon; red internal reflections

Crystal habit

Tabular prismatic crystals, also as finely granular masses

Cleavage

Good on {1011}

Mohs scale hardness

5 – 6

Luster

Sub-metallic

Streak

Purplish brown

Diaphaneity

Opaque to translucent

Specific gravity

3.79 – 4.2

Optical properties

Uniaxial (-)

Refractive index

nω = 2.310 – 2.350 nε = 1.950 – 1.980

Birefringence

δ = 0.360 – 0.370

Pleochroism

Weak, O = pinkish red, E = brownish to purplish red

References

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.

It was first described in 1892 for an occurrence in the Ceylonese gem bearing gravel placers. It was named for Scottish geologist Sir Archibald Geikie (1835–1924). 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.

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