Armalcolite

Formula:  (Mg, Fe)Ti₂O₅

Origin of name:  For the 3 astronauts of Apollo 11, Neil A. Armstrong, Edwin E "Buzz" Aldrin and Michael Collins, who collected it from Tranquillity Base on the Moon

Crystal system:  Orthorhombic

Crystal class:  2/m /2m 2/m

Twinning:

Unit cell: a = 9.743 Å, b = 10.023 Å, c = 3.738 Å

Colour:  Gray, grey to tan in reflected light

Diaphaneity: Opaque

Luster: Metallic

Habit:  Microscopic embedded subhedral to anhedral grains, usually with rectangular section

Hardness: <5

Specific gravity:  4.94

Cleavage:  None

Tenacity:

Streak:

Synonyms/varieties:

Comments: Formed typically at low pressures and high temperatures; in Ti-rich basalts and microbreccias of lunar samples; in salic volcanics; rarely in granite pegmatites; in ultramafic rocks, lamproites, kimberlites, in terrestrial impact craters; in inclusions in a carbonaceous chondrite.