Seylan Gems & Jewelry
Spinel is its own mineral, not a kind of sapphire. For centuries red spinel was sold as ruby because the eye cannot always separate them. A refractometer can: spinel is singly refractive, corundum is not.
Specifications
Typical published ranges used in gemology. Specific gravity below matches our carat calculator default where applicable. (SG 3.60)
| Hardness (Mohs) | 8 |
|---|---|
| Refractive index | About 1.718 (typically 1.712–1.736) |
| Optic character | Singly refractive (isotropic) |
| Specific gravity | About 3.60 |
| Chemistry | MgAl₂O₄, with color from trace elements such as chromium, iron, or cobalt |
| Lustre | Vitreous |
Red spinel can be a vivid crimson. Pink, lavender, blue, and cobalt-blue stones are collected for their own look, not as stand-ins. Cobalt-blue spinel is a color description of the stone, not a brand. Judge the face-up color in daylight and under indoor light. A stone that only looks rich in one lamp may disappoint in the other.
Clarity is often higher than in emerald. Inclusions, when present, can be octahedral crystals or iron stains. They are part of the stone’s story. They are not, by themselves, a clarity grade.
Sapphire and ruby split light into two rays. Spinel does not. That single fact is why a refractometer reading and a polariscope check are more useful than a side-by-side photo. Specific gravity is also lower than corundum: about 3.60 versus about 4.00. A carat of spinel therefore shows a bit more face-up size than a carat of sapphire of the same cut proportions.
Heat is not the routine trade treatment it is for sapphire. Many spinels are sold unheated. If a listing says unheated, that is a claim about that stone, not a promise about every spinel on earth. Ask us if you want the wording on a particular item explained.
Read the millimetre measurements, not only the carat weight. Use the carat calculator with the spinel default if you are checking whether a weight is plausible for the size. On the product page, use Size & Fit so the footprint is clear before you commit.
Ceylon is an important source for spinel, which is why you will see it often in our catalog. Origin on a listing should match the description of that item. We do not treat origin as a slogan.
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