Spinel suffers a bit from the underserved negative connotation associated with it. The bad rap likely comes from two facts: i) synthetic, laboratory-created, spinel has been on the market for quite some time; and ii) it was often used as a ruby simulant.
But I am continually impressed by the beautiful, brilliant, colours that natural spinel can produce and continually endeavour to have some in my inventory. I may even have a project or two in mind for personal jewellery (ring) item.
You might have read elsewhere on this Web site my playful lament that life would be much simpler if all green gems were emeralds, all blue gems sapphire and all red gems ruby. Unfortunately, a number of groups or families of stones can produce similar colours. A red stone, therefore, can be either a ruby, a spinel, a garnet, or a beryl, for example.
Spinel is another group of gemstone that can produce a variety of colours. More on that below.
Spinel has very good wearability; meaning it is both hard and can withstand normal wear-and-tear.
Appearance to the naked eye:
Few buyers go into a retail stores with a loupe and gemological tools in tow. They rely on how appealing the gem is to them purely from a visual perspective. And this is also the case when you are out to dinner or in a social gathering – it is highly unlikely that the other guests are using sophisticated laboratory tools to admire your ring; instead they are relying on what they see with their naked eyes. That is why we want to spend a bit of time explaining what it is you can expect to see just by eyesight.
Every colour possible. Red, blue and yellow colour hues are most prevalent. Browns, greens, and blacks are also possible; as are pinks, oranges, purples and everything else in between.
Transparent to translucent
Four-point and six-point star features are possible (also known as asterism)
Spinel can present ghost crystals. This is one spinel crystal grows faster and eventually engulfs another spinel crystal; thereby trapping the smaller crystal inside the larger one. The smaller crystal can sometimes be observed by the naked eye or under magnification.
Other interesting facts:
The Black Prince’s ruby in the Crown Jewels, which is one of the oldest Crown jewels of the United Kingdom in the middle of the 14th century (ref: Wikipedia) is not a ruby but rather a spinel. The mis-identification was only discovered centuries later. That, in itself, should be testament to the beauty that spinel gem material can produce.
Spinel has been synthetically produced since the early 1900’s.
- Optical character and sign:
isometric (single refractive)
- Refractive Index:
1.710 to 1.735 range or greater; depending on the colour
None – stone is isometric
- Optic Character:
double refractive, uniaxial, negative: U-
- Conoscope image:
- Hardness (Mohs scale):
7.5 to 8.0 depending on colour
- Specific gravity:
3.54 to 4.1 range depending on colour
tenacious to wear-and -tear
- Spectral absorption:
- Polariscope reaction:
Spinel is single refractive so there would be no extinction.
There are reports that synthetic spinel can produce an anomalous double refractive (ADR); also known as tabby extinction.
- Chelsea filter reaction:
- Dichroscope reaction: