Spinel Quality Factors
Spinel comes in a variety of colours, but the most commercially important are red and pink. Mauve- or lilac-coloured spinels are also attractive, and some blue spinel colours can be intense.
Some spinel colours are more rare and valuable than others. In general, red spinel is the most desirable, followed by fine cobalt-blue spinel, then by vibrant hot pink and vivid orange stones. Violet and bluish purple to purple, or lavender, stones tend to be less attractive, and less in demand than other, rarer colours.
Red spinel ranges from orangey red to purplish red, with pure red to slightly purplish red hues of medium to medium-dark tone considered the finest of all. A top-quality 5-ct. red spinel might sell for around a tenth the price of an equivalent-quality ruby, and pink spinel often sells for less than pink sapphire.
Spinel has been making a name for itself over the last couple of decades, and demand for fine stones well exceeds supply. In fact, spinel is in great demand among gemmologists and gem connoisseurs. This has, to some degree, closed the spinel vs. ruby-and-sapphire price gap.
Blue spinel hues range from violet blue through very slightly greenish blue.
Most stones have low saturation, and the blue hues take on a distinctly greyish look. The best and most highly valued blue spinel colours parallel blue sapphire, with intense violet-blue to pure blue colours that are neither too dark nor too light.
Spinel that has no inclusions visible to the eye is more valuable than spinel with inclusions that can be seen. The more visible any inclusions are, the more the value drops.
Spinel can have some very beautiful inclusions that reflect the gem’s usual octahedral crystal growth. Some appear in groups that resemble human fingerprints.
Spinel is cut in a variety of shapes and cutting styles. As with many coloured stones, ovals and cushion shapes are very popular.
Because of the scarcity of spinel on the market, most fine-quality rough is cut in non-standard sizes to save weight, instead of in standard industry sizes. The standard-cut, or calibrated, stones that are available tend to be mixed-cut ovals, usually in 6×4-mm and 7×5-mm sizes, suitable for centre stones in rings. Commercial qualities are more commonly cut to standard sizes for jewellery.
Larger spinel sizes rise considerably in per-carat price. Availability drops and prices rise sharply for fine red, pink and blue stones above five carats.