Armalcolite
(Mg,Fe2+,Al)(Ti4+,Fe3+)2O5 [CNMNC approved formula]
Named in 1970 after the three astronauts of Apollo 11: Neil A. ARMstrong, Edwin E. "Buzz" ALdrin, and Michael COLlins, who collected it from Tranquillity Base on the Moon.
| IMA status : | Redefined IMA Approved; 1988 (IMA1970-006) |
| CLASSIFICATION | |
| Dana (8th edition) : |
07.07.01.02 |
| (07) Multiple Oxides | |
| (07.07) with miscellaneous formulae | |
| (07.07.01) | |
| Nickel-Strunz (10th edition) : |
04.CB.15 |
| (04) Oxides and Hydroxides | |
| (04.C) Metal:Oxygen = 2:3, 3:5, and Similar | |
| (04.CB) With medium-sized cations | |
| Crystal system: | Orthorhombic System |
| Point group (H-M): | mmm (or 2/m 2/m 2/m) — dipyramidal |
| Unit cell: | a = 9.743 Å, b = 10.023 Å, c = 3.738 Å |
| Crystal Habit: | Microscopic embedded subhedral to anhedral grains, usually with rectangular section |
| Color: | Gray, gray to tan in reflected light |
| Diaphaneity: | Opaque |
| Luster: | Metallic |
| Hardness (Mohs): | 4.9 |
| Measured Density: | 4.94 g/cm3 |
| Geologic Setting: | Formed typically at low pressures and high temperatures; in Ti-rich basalts and microbreccias of lunar samples; in salic volcanics; rarely in granite pegmatite; in ultramafic rocks, lamproites, kimberlites; in terrestrial impact craters; in inclusions in a carbonaceous chondrite. |
| Mineral Association: | Ilmenite, Fe–Ti oxides, iron, graphite (Disko Island, Greenland); phlogopite, analcime, diopside (Smoky Butte, Montana, USA); rutile, ilmenite (Kimberley, South Africa) |
Gray semi-metallic armalcolite micro crystals on coal.Origin: Chelyabinsk Oblast', Urals Region, Russia.
Photo: © Rruff Project