Mineral Information and Data:

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)
  

 

Armalcolite
Gray semi-metallic armalcolite micro crystals on coal.
Origin: Chelyabinsk Oblast', Urals Region, Russia.
Photo: © Rruff Project

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