Synteettisen flux-menetelmällä kasvatetun punaisen spinellikiteen pintakuvioita. — Photo: Sepelinmurskaaja · CC BY-SA 4.0
Spinel
Also known as: Ruby spinel, Balas ruby.
Magnesium aluminate — the cubic oxide whose pointed crystals gave it the name; red spinels were long mistaken for rubies.
Intro adapted from Wikipedia (CC BY-SA).
Spinel is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula MgAl₂O₄.
It crystallizes in the cubic crystal system (space group Fd3m). It is a member of the Spinel structural group.
Key properties: Mohs hardness 7.5–8; specific gravity 3.6–4.1; typically red or blue or green or black or brown or purple or pink or colorless; White streak; Vitreous, splendent to dull luster; refractive index 1.719; optically isotropic.
IMA symbol Spl, grandfathered status — known before the IMA’s founding.
A common mineral, formed at high-temperatures as an accessory in igneous rocks, principally basalts, kimberlites, peridotites, and in xenoliths; in regionally metamorphosed aluminum-rich schists.
It is found associated with Forsterite, chondrodite, scapolite, phlogopite, corundum, sillimanite, andalusite.
Perhaps from the Latin spinella, for little thorn, in allusion to the spine-shaped octahedral crystals.
Collections: Gemstones, Collector Favorites.