About Spinels
For the better part of a thousand years, the spinel was mistaken for ruby. The Black Prince's Ruby, the great cabochon set in the front of the Imperial State Crown of the United Kingdom, was identified as a spinel only in the nineteenth century; the Timur Ruby of the same collection, a 361-carat polished bead inscribed with the names of six Mughal emperors, is likewise a spinel. The two minerals occur together in many of the same deposits, share a similar deep-red appearance, and resisted scientific differentiation until the rise of modern crystallography and refractive-index measurement. The result is that spinel has spent most of its history in the shadow of corundum — a circumstance that the gem trade has recently begun, energetically, to reverse.
Spinel is magnesium aluminium oxide (MgAl2O4), an isometric (cubic-system) mineral chemically and structurally distinct from corundum, with a Mohs hardness of 8, a refractive index of 1.712 to 1.736 (singly refractive, in contrast to corundum's strong birefringence), and a specific gravity of approximately 3.60. The pure mineral is colourless; trace chromium produces red (in concentrations that can rival the finest Burma ruby in saturation), trace iron produces violet through purple to black, and trace cobalt produces a cobalt-blue of exceptional saturation and rarity. The hot-pink spinels of the Mahenge deposit in Tanzania, discovered in 2007, are now among the most coveted coloured stones in the international market — the most intense Mahenge material has been marketed in the trade as “Jedi” spinel and can command per-carat prices exceeding twenty thousand US dollars in fine sizes.
The classical sources for fine red spinel are the Mogok and Namya deposits of Upper Burma — the same geological province that produces the world's finest rubies — and the historic Kuh-i-Lal deposit in the Pamir mountains of present-day Tajikistan, which supplied the “balas rubies” of medieval Europe. The Mogok material includes the legendary “hot pink” and “red-orange” tones that compete directly with fine ruby in colour quality, and AGL's Sri Lanka laboratory regularly examines significant volumes of Mogok spinel passing through the South Asian trade. Origin determination is supported by LIBS trace-element analysis (chromium, vanadium, iron, and gallium are particularly diagnostic) and inclusion-pattern study, with Burma material typically showing octahedral negative crystals and apatite inclusions that are uncommon in other deposits.
Treatment is the great selling point of spinel. Unlike corundum, the spinel market is dominated by natural, untreated material; heating spinel produces unpredictable colour results and is uncommon in the trade, and no fracture-filling, diffusion, or coating treatments are currently in commercial use. The AGL spinel certificate therefore tells a buyer three things of immediate value: confirmation that the stone is natural spinel (not synthetic, not ruby substitute), the heat-treatment status (which on the vast majority of submissions is “No indications of heating”), and the country of origin where analytically supportable. For buyers seeking the depth and saturation of fine red corundum without the corundum price tag — or seeking the cobalt-blue or hot-pink colours that corundum does not naturally produce — spinel offers an analytically clean, scientifically defensible alternative.
How AGL certifies Spinels
Every spinels submitted to an AGL laboratory is examined by at least two senior gemologists and analysed using our standard instrumental package: refractive-index and specific-gravity measurement, microscopic examination under dark-field and fibre-optic illumination, UV-VIS-NIR absorption spectroscopy, FTIR spectroscopy for treatment detection, and LIBS or ED-XRF for trace-element analysis where origin is in question. Every conclusion on the certificate — species, variety, treatment, origin — is supported by recorded analytical data, and every certificate is recorded in our secure verification database for online authentication at any time.
For full service descriptions and turnaround times, see our Services page, or contact your nearest AGL laboratory for a written quotation.
