Spinel Price per Carat: What Sellers Ask, by Colour

Each line quotes at least three sellers, in their own size bands. Amounts are US dollars per carat.

Fine red is a separate market. The Natural Gemstones Company lists $8,000 to $15,000 for red over 5 carats, The Rare Gemstone Company says fine larger reds fetch over $8,000, and Gem-Matrix quotes $5,000 to $15,000 for high-quality Burmese red.

Where the guides disagree, they disagree by a lot. For 1 to 2 carat cobalt blue, Melogems puts top quality at $500 to $1,000, while The Natural Gemstones Company puts medium blue at $1,000 to $2,500. Read every range as one seller’s opinion, not a quote. Our own prices are not in the table for that reason.

Colour, by a distance. Per GIA, red is the most desirable spinel, followed by fine cobalt blue, then vibrant hot pink and vivid orange. Violet, bluish purple and lavender stones are less in demand, and purple and violet stones typically sell for around half the price of a pink spinel of similar quality.

A trace element does the colouring. Chromium gives intense reds and pinks, and the more chromium, the stronger the red. Iron alone gives a low-saturation violet or grey-violet: attractive, but rarely fine. Most blue spinel owes its colour to iron and looks greyish. A mix of cobalt and iron makes the rare, vibrant cobalt blues, which are much more desirable.

So the word “pink” covers a wide range. The guides above run from $200 to over $4,000 a carat for it, and the depth of colour is the first thing to look at.

Size matters most at the top. Gem-quality spinel is hard to find above 5 carats, and for fine red, pink and blue stones above five carats availability drops and prices rise sharply, per GIA. Gem Rock Auctions, The Natural Gemstones Company and Melogems all publish higher figures per carat as weight goes up.

Yes. Spinel crystals are often flattened twins, so cutters make shallow stones to avoid losing weight. Large tables and windows, together with shallow crowns and pavilions, are the signs of weight retention, per GIA.

A shallow stone carries more carats than it shows face-up, so a price per carat can look kind while you pay for weight you cannot see. When you compare two quotes, look at both stones face-up in daylight and compare the size you see, not only the carats.

When a clean, saturated stone is priced far below the ranges above, ask what it is before you ask about the price. Spinel is rare and synthetic spinel is common, so many people have never seen the natural stone, per GIA. Synthetic spinel first appeared by accident in the early twentieth century, when researchers were trying to grow blue sapphire, and it has stood in for sapphire, zircon, aquamarine and peridot ever since. A flux-grown version followed in the 1990s, in colours including red.

An independent lab report settles it. Our guide to what a gemstone certificate proves explains what a report does and does not tell you.

1. Name the colour. Red, pink, blue, cobalt blue or purple: each has its own line above. A quote of “spinel, 3 carats” says almost nothing.
2. Ask where the number comes from. A seller’s guide is that seller’s opinion. Ask for the stone’s own price, weight and photographs.
3. Look at the stone face-up, in daylight, tilted. Check the window in the centre, the fractures and the colour zoning.
4. Ask for a lab report on anything sold as fine red or cobalt blue. Those descriptions carry the highest prices.

Two neighbouring pages help: blue spinel versus blue sapphire, and the complete spinel guide for the species itself.