Geikiélite - Encyclopédie

GEIKIELITE

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Trigonal
    Chemistry : MgTiO3
    Rarity : Rare to uncommon

Geikielite belongs to the ilmenite group of which it constitutes the magnesian term. There is also a complete solid solution towards the iron pole, ilmenite itself. It is a mineral typical of the contact metamorphism of dolomites and magnesium limestones, as well as very magnesium rocks, such as serpentinites, kimberlites and sometimes carbonatites. It is also present in alluvial deposits, notably diamondiferous placers resulting from the dismantling of kimberlites : geikielite is thus a diamond tracer mineral. It was named in honor of the Scottish geologist Sir Archibald Geikie. Geikielite normally occurs in tumbled grains, very rarely in tabular to prismatic crystals of 25 mm maximum. Geikielite is black or very dark brown.


Main photo : Geikielite from Monte dei Tre Abati, Coli, Piacenza Province, Italy © Serge Lavarde

Geikielite on carbonatite from Malyi Murun Massif, Irkutsk Oblast, Russia © C. Boutry
Geikielite from Mount Somma, Vesuvius, Italy © Chinellato Matteo
1.1 cm geikielite from Rakwana, Ratnapura, Sabaragamuwa, Sri Lanka © Dan Weinrich
Geikielite on marble from Amity, Warwick, New York, USA © Glenn Rhein

Geikielite in the World

Large centimeter-sized crystals come from Skeleton Canyon (Arizona), Crestmore marbles (California), and Wakefield (Quebec) where geikielite is associated with large crystals of diopside and hydromagnesite. Russia is also home to several deposits that have provided beautiful geikielite crystals, notably the chromiferous serpentinite of Jemoracly-Tube, in the Causase, and the Camel Mountains in the Southern Urals. Rare small crystals have been described in Bergell (Swiss Alps). Geikileite is present in the Jagerfontein kimberlite, near Kimberley (South Africa) and in the gem-bearing placers of Sri Lanka. Small automorphic crystals are also known in the projections of Vesuvius (Italy).

Geikielite in France

In France, geikielite is reported in the mines of Costabonne (Pyrénées-Orientales).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 5 to 6
Density : 3.8 to 4.2
Fracture : Conchoidal
Streak : Purple brown

TP : Translucent to transparent
RI : 1.950 to 2.350
Birefringence : 0.360 to 0.370
Optical character : Uniaxial -
Pleochroism : Low
Fluorescence : None

Solubility : Hydrochloric acid


Magnetism : None
Radioactivity : None

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