Spinel

Spinel is a mineral species, the magnesium and aluminium oxide that lends its name to the wider spinel group. It grows as cubic crystals, most often twinned octahedra, and rates about 8 on the Mohs scale. It may lack colour altogether, though red, lavender, blue, green, brown, black and yellow stones are the usual run; chromium causes the red of Burmese stones and a little cobalt the pure blues. The name comes from a Latin word for a little spine, after its pointed crystals. Spinel forms in the same kinds of rock as corundum, so spinel and ruby commonly turn up side by side, and before ruby had a scientific definition red spinel was called ruby too: two of the great red stones among Britain's Crown Jewels, the Timur Ruby and the Black Prince's Ruby, are spinels. Old names for the red stones were spinel ruby and balas ruby, the second after Badakhshan in central Asia, whose mines in present-day Tajikistan were for centuries the chief source. Cheap synthetic spinel is cut for August birthstone jewellery and used to imitate aquamarine and emerald. Cunningham assigns spinel to Pluto and fire and uses it to lend the body energy, to add physical strength during hard exertion, and in spells for riches and wealth. Hall connects it with renewed energy, encouragement and rejuvenation, and with accepting success humbly.