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The gemstone spinel


#1

Spinel is most famous for its deep red variety that closely resembles Ruby. These two gemstones can be very difficult to distinguish. Until the late 19th century, there was no distinction made between Ruby and red Spinel, as they look identical and are found in the same localities. Many famous old “Rubies” were discovered to be in fact Spinel. For example, the enormous “Ruby” that forms the centerpiece of the royal crown of England (the Black Prince’s Ruby) was actually determined to be Spinel.

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#2

The idea that spinel and ruby were indistinguishable is a widely held myth. In fact, Al Tifaschi, (11th Century), Juan Arfe de Villafane (1571) and J. B. Tavernier (1678) all made the distinction between ruby and spinel. Tavernier, in fact, tells the story about the Indian Emperor Aurangzeb who received a large red gem, but suspecting it to be spinel, sent it to his father, the famous Shah Jahan, who he had deposed and imprisoned in the Red Fort at Agra. Shah Jahan identified it as spinel and valued it at a 10th of the value of a true ruby. Juan Arfe de Villafane put together a price list that compared ruby and spinel. See my Secrets Of The Gem Trade (2nd edition) www.secretsofthegemtrade.com

Spinel first became available in the 10th century and very much valued in Europe until the 18th Century when its value relative to ruby began to decline. European monarchs vied with one another for the largest gems. The liked big! Spinel or Balas ruby fit the bill. As Ceylon Gemstones mentions, many large spinels were simply called ruby including The Black Prince’s stone and Catherine The Great’s stone which I saw some years back and believe is actually a tourmaline.

RWW


#3

Further to Richard W Wise’s references, spinels are well documented in literature in the sixteenth century:

There is also… an other kynde of Rubies which wee caule Spinelle.
(Eden, 1555)1

There is a great store of rubies, saphires, and spinelles in this Iland.
(Hakluyt, 1599)2

1	R. Eden, The decades of the newe worlde or west India; p. 264. 1555 (reprinted 1885).

2	R. Hakluyt, The principall navigations, voiages and discoueries of the English nation; p. 264. 1589 (reprinted 1598–1600).

#4

Nice to see the distinguished Mr. Wise posting here. To amplify on what he said, the separation of ruby from spinel is nearly trivial. If you are any good at visual optics, the “rainbows” seen in ruby will be somewhat doubled due to double refraction, whereas spinel, being singly refractive, shows only one ROYGBIV rainbow that is not overlapped with another one. If you place the gem on a typical cell phone or laptop screen and view it through a polarized sunglass lens, you will have a polariscope and can do the test for SR vs DR. Ruby=DR, Spinel=SR. Synethtic spinell may show a patchy ADR (anomalous double refraction) which makes it hard to distinguish from the doubly refractive ruby. Also, ruby is dichroic and should show two slightly different shades or red, whereas spinel shows only one shade no matter which direction you look at it in.

I should clarify that the above will separate ruby from non-ruby, but an SR red stone could still be either spinel or garnet. UV fluorescence of red spinel and magnification of inclusions will separate spinel and garnet, as will SG for some garnets. A little gemology knowledge goes a long way in this case. Hope this is of help.
royjohn
Also, there is often (not always) a brown color modifier for red garnet, but not usually for spinel.