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Formula: MgTiO3
Simple oxide, ilmenite group,
titanium-bearing mineral, forms a series with
ilmenite
Crystal System: Trigonal
Specific gravity: 3.79 to 4.2 measured, 3.895 calculated
Hardness: 5 to 6
Streak: Purple-brown
Colour: Black, red, brownish black
Solubility: When in a fine powder, geikielite is slowly decomposed by hot strong hydrochloric acid. It is also
decomposed by hydrofluoric acid even in the cold in the course of a few hours if finely powdered (Mindat)
Common impurities: Fe,Cr,Mn,Ca
Environments
Igneous environments
Carbonatites
Metamorphic environments
Geikielite forms during contact metamorphism of impure magnesian
limestones. Also in
carbonatites,
kimberlites, serpentinised
ultramafic rocks, and in gem-bearing placer deposits. Associated minerals include
rutile, spinel,
clinohumite, perovskite,
diopside, serpentine,
forsterite, brucite,
hydrotalcite, chlorite and
calcite
(HOM)
Localities
At the type locality, Rakwana, Ratnapura District, Sabaragamuwa Province, Sri Lanka, geikielite occurs as pebbles in
gem gravels, associated with rutile
(Mindat).
Amity, Town of Warwick, Orange county, New York, USA, is an area of
granite intrusions into
marble and associated
gneiss. The marble is
mostly composed of white crystalline calcite that often has small flakes
or spheres of graphite and
phlogopite.
Geikielite is a relatively rare titanium mineral that is the magnesium analog
of ilmenite and pyrophanite. It occurs
here
in small, rounded grains with a metallic lustre in association with dark red spinel and
magnesio-hastingsite in weathered
marble
(R&M 96.5.437).
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