Geikielite
MgTiO3 [CNMNC approved formula]
Named in honor of Sir Archibald Geikie (1835–1924), Scottish geologist and Director-General of the Geological Survey of Great Britain.
| IMA status : | Valid species (Pre-IMA 1892) Grandfathered |
| CLASSIFICATION | |
| Dana (8th edition) : |
04.03.05.02 |
| (04) Simple Oxides | |
| (04.03) with a cation charge of 3+ (A+++2 O3) | |
| (04.03.05) Ilmenite Group | |
| Nickel-Strunz (10th edition) : |
04.CB.05 |
| (04) Oxides and Hydroxides | |
| (04.C) Metal:Oxygen = 2:3, 3:5, and Similar | |
| (04.CB) With medium-sized cations | |
| Crystal system: | Trigonal System |
| Point group (H-M): | 3 — rhombohedral |
| Space group: | R3 |
| Unit cell: | a = 5.05478(26) Å, c = 13.8992(7) Å, Z = 6 |
| Crystal Habit: | As tabular and prismatic crystals, showing {0001}, {1011}, {2025}, {0221}, to 2.5 cm; more commonly subhedral to anhedral, and as irregular to rounded grains. |
| Color: | Black, less commonly ruby-red; in transmitted light, brownish to purplish red; gray in reflected light, with red internal reflections |
| Diaphaneity: | Opaque to translucent |
| Luster: | Submetallic |
| Hardness (Mohs): | 5 - 6 |
| Measured Density: | 3.79 – 4.2 g/cm3 |
| Cleavage: | {1011} |
| Fracture: | Conchoidal to subconchoidal |
| Streak: | Purplish brown |
| Polymorphism and Series: | Forms a series with ilmenite. |
| Geologic Setting: | Forms during contact metamorphism of impure magnesian limestones. Also in carbonatites, kimberlites, serpentinized ultramafic rocks, and in gem-bearing placer deposits. |
| Mineral Association: | Rutile, spinel, clinohumite, perovskite, diopside, serpentine, forsterite, brucite, hydrotalcite, chlorite, calcite. |
Origin: Monte dei tre Abati, Coli, Piacenza Province, Emilia-Romagna, ItalyPicture size: 2.2 mm
Photo and owner: Thomas Witzke
Black crystals in calcite matrixOrigin: Murun, Yakutia, Russia
Sample size: micromount
Photo: Diederik Visser