No products in the cart.
Photo 1- Rough, with a clear octahedral form. Only the tiny octahedron is quality cutting.
Photo 2 – Wisteria (light lavander) spinel; these stones take on different colors with natural or artificial light.
When you present an unqualified person with a batch of spinels, the following wisecrack is unavoidable: “then I’ll almost have a joint“: (literally ‘spinello’ in italian), alluding to cannabis in the form of marijuana or of hashish. An unfortunate name then, that has nothing to do with it, ambiguous in its meaning.
Its hardness from here on! Topaz deserves a place of its own on the Mohs scale; spinel is also declared as having 8 in hardness, no. Even in its hardness it is ill-starred!
And the colors! When it expresses itself in its most beautiful colors, cornflower blue, sky blue, salmon pink, blood red, light lavander, purple violet, it is virtually indistinguishable to the naked eye from the most beautiful sapphires and rubies! The most typical red ones are in the same gem gravels as the rodolite garnets; they have the same color, and special instruments have to be used to distinguish between them.
The rubies and sapphires of many famous jewels, are, in fact, spinels. Superb colors, but too similar to those of other stones! Specifically spinel can boast a few exclusive colors; an ink blue, a strong violet, an almost black blue (very similar to schiorlite or black tourmaline), a brick red which is far too dark. Spinel is mono-rifrangence. But it has a “anomalous birefringence”, so at first glance it looks as if it were birefringent. A chameleon stone, looking for its space stealing this from other stones. The industry has treasured its attitude to be so similar to other stones, and artificially produced it in large quantities, imitating almost all natural stones. Ironically, the refractive index of the synthetic spinel is slightly higher than that of the natural spinel! And the anomalous birefringence: with a polariscope, ragged silk shades appear; while in the natural, swaying silk veils are seen.
Photo 1 – Cinnamon spinel. This stone is very similar in appearance to hessonite garnet.
Photo 2 – Hot pink in a fine spinel specimen of about seven carats.
Photo 3 – Superb cardinal purple in a splendid specimen of about ten carats. Photo 4 – Spinel, while crystallizing in the cubic system, can present the optical phenomenon of a star with six rays, just like sapphire.
I had bought a batch of spinels, and with the lupe, I noticed three spherical bubbles in one of the stones. Panic attack! Because the inclusions of spherical bubbles are an exclusive prerogative of synthetic stones; natural stones have sharp-cornered crystalline inclusions. Under a microscope, the bubbles continue to be spherical! I increase the magnification, I bathe the stone in a smelly liquid, 1-bromonaphthalene, which serves to eliminate the effects of refraction, and examine it in detail. It is still spherical, a bubble. Only that it is inserted inside a perfect hexagon! These inclusions are called “two-phase” and are made up of a negative crystal (i.e. from the ‘fingerprint’ of a crystal that is not there), and a liquid bubble. In some cases, also a tiny crystal may be present, than these are “three-phase” inclusions. When you encounter inclusions of such beauty, which resolve rather involving gemological doubts (natural stone or synthetic?); well, there can only be upmost thrill and enjoyment.
What a strange stone! The finest red spinels are those of Burma, and are located in the same pit of the rubies; the best blue ones are found in Sri Lanka, of course they are intermixed with sapphires; in India spinels are purple-ink in color, together with the same color of the iolites. They are also found in Sri Lanka, location Matara, in rodolite garnet quarries, where they have the same color. Sometimes zircon assumes a very special deep red color; spinel also manages to have that same color. There is also a rather rare variety of orange, similar to hessonite garnet. Of course, the light blue color does not look like the clear sapphire, but like acquamarine. To say it all, there are also rare examples of star spinels with six light rays, similar to star sapphires and rubies. All stones have their own personalities; that of the spinel is expressed by it mingling with the crowd of other stones. This is a weird role for a stone. A performance similar to that of an actor who embodies the most varied members. For this reason we think it is the most suitable stone for actors, comedians, entertainers, writers, and why not, for all those who, in life, love doubt, role reversal, and who live their adventure on this earth as if they were on a big stage, where it is not clear on which side are the actors and on which the audience.
Specifications
CRYSTALLIZATION: monometric system.
CHEMICAL COMPOSITION: magnesium aluminates.
CHEMICAL FORMULA: MgAl2O4
GENERAL CHEMICAL FORMULA: R “O.R” ‘O3 (R’ = Mg, Fe, Zn, Mn; R ” ‘= Al, Fe, Cr, Mn)
HARDNESS: 8. It usually cuts topaz, without being influenced by it; so its hardness is slightly higher than 8.
DENSITY: 3.60 approximately (depending on the elements that compose it; the zinciferous quality may exceed 4).
REFRACTION: singly refracting.
REFRACTIVE INDEX: from 1,714 to 1,722.
COLORS: almost all hues are expressed by the spinel; even green (very similar to the best tourmaline), in ‘clorospinel’ and in ‘chromospinel’.
SOURCES: Burma, Siam, Sri Lanka, Madagascar, Brazil, India, Russia.
SYNTHESIS: reproduced not in imitation of the spinel, but as a duplicate of almost all other precious stones. Synthetics generally have a higher refractive index (from 1.720 to 1.730), and an odd birefringence which, under cross polarized light (CPL), results in the ‘anomalous extinction effect’, a pattern of light and dark extinction zones, bands or cross shapes may be seen, which may move across the stone on rotation. This effect, literally ‘of the ragged silk’ from the italian, is due to internal strain in the material which causes a certain amount of anisotropy in an otherwise isotopic structure. The first syntheses dates back to the middle of 1800
