Geikielite Locality: Maxwell quarry, Chelsea , Les Collines-de-l'Outaouais RCM, Outaouais , Québec , Canada ( Locality at mindat.org ) Size: 7.5 x 6 x 4 cm. Geikielite is a rare magnesium titanium oxide, found usually in microcrystals or masses. It is the magnesium analogue of Ilmenite. Here we have a huge mass of geikielite about 3 inches in size with distinct big crystals over 1 cm in size embedded within it. It shows metallic lustre and some sharp twinning. This has been confirmed via communications with several collectors of rarities and the Royal Ontario Museum. Ex. Philadelphia Academy of Sciences Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Geikielite
A magnesium-titanium oxide of the ilmenite group — opaque black trigonal crystals.
Intro adapted from Wikipedia (CC BY-SA).
Geikielite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula MgTiO₃.
It crystallizes in the hexagonal crystal system (space group R-3). It is a member of the Corundum structural group.
Key properties: Mohs hardness 5–6; specific gravity 3.79–4.2; Purplish brown streak; Submetallic luster; refractive index 2.155; optically uniaxial.
IMA symbol Gk, grandfathered status — known before the IMA’s founding, named in 1893.
Forms during contact metamorphism of impure magnesian limestones. Also in carbonatites, kimberlites, serpentinized ultramafic rocks, and in gem-bearing placer deposits.
It is found associated with Rutile, spinel, clinohumite, perovskite, diopside, serpentine, forsterite, brucite, hydrotalcite, chlorite, calcite.
In honor of Sir Archibald Geikie (1835–1924), Scottish geologist and Director-General of the Geological Survey of Great Britain.