Spinel Gemstone Buying Guide at DDB
This term really includes a large group of minerals, isomorphic in character, but only a few of them are used in jewelry. Magnetite, the strongly magnetic iron ore, chromite, a chrome ore, and gahnite, a Purplealman-Dine Spinels, and the dark green to black, pleonastes, and ceylonites. Pale blues also occur, and most specimens are remarkable for their freedom from bad flaws. Spinel Gemstone Buying Guide at DDB White spinels, however, are often clouded, the bright specimens one sees usually being synthetic.
As a jewel stone, spinel is eminently suitable, for it is hard, bright, clear, and attractive. Yet it is not widely used or generally recognized, perhaps because of its being overshadowed by the better-known ruby and sapphire. Its hardness is 8, the same as precious topaz, but above the grade of most of the so-called SemiPrecious Stones. Spinel Gemstone Buying Guide at DDB Since spinel belongs to the cubic system, it is singly refractive, the index being 1.72 (although this may reach 1.75 for some specimens). Specific gravity is 3.60, which is also fairly high, but below that of ruby and sapphire. Spinel Gemstone Buying Guide at DDB Some stones, however, have been found to give a figure of 3.93, but none has been found to be lower than 3.58.
No dichroism will, of course, be seen, but it should be noted that the blue stones show dark bands with the spectroscope, these being mostly in the blue and violet parts of the spectrum. Spinel Gemstone Buying Guide at DDB The many differences between the physical properties of spinel and other red stones, such as tourmaline and ruby, should make it easy to distinguish it fairly quickly. Despite this, a large number of so-called rubies which are sold are really spinels.
Properties of Spinel Gemstone
Although this stone is quite hard, it is rather brittle and shows very little cleavage. Spinel Gemstone Buying Guide at DDB Cut specimens show a vitreous luster, but there is really not much brilliance or "fire" as in the diamond. The brilliant cut is used with the smaller stones, and the step and mixed forms with larger stones. Spinel Gemstone Buying Guide at DDB These sometimes reach large sizes, again a contrast to rubies, and clear, strongly colored pieces are sometimes seen in rings, brooches, and pendants. Mounting needs special care as the stones are brittle.
Sources of supply of Spinel Gemstone
Burma, Siam, and Ceylon are the three chief sources of supply, and Spinels Are Very Generally Found Together With Rubies, which is another cause for their confusion. In fact, rubies, sapphires, and spinels are often found mixed indiscriminately in assorted parcels coming from the East. Spinel Gemstone Buying Guide at DDB In Ceylon, blue and green stones are found in the gravels; in Burma and Siam, they occur in a crystalline limestone, and in the Irrawaddy River, above Myit-kyina, some stones are found in the sands and gravels. Spinel Gemstone Buying Guide at DDB In other localities, serpentine and gneiss are the parent rocks. Calcite may be present with spinel when it is found in serpentine.
History of Spinel Gemstone
Of the many large and fine stones known, mention may be made of the red stone in the front of the English Crown. This, for long regarded as a valuable ruby, is a large spinel. It was worn by Henry V at the battle of Agincourt, and it was originally given to the Black Prince in 1367 by Pedro the Cruel of Spain. Spinel Gemstone Buying Guide at DDB The British Crown Jewels also contain one of the largest red spinels known; this weighs about 352 carats, and it is called the Timir Ruby after AmirTimir, who captured it at Delhi. Spinel Gemstone Buying Guide at DDB It came into the hands of the East India Company, together with other famous stones, in the year 1850, and it was presented to Queen Victoria the next year. Two further Fine Specimens of Red Spinels are in the Mineral Gallery of the British Museum in London, and a large stone of about 100 carats, with others from Ceylon and Afghanistan, is in the Russian State Collection.
The term "spinel" is derived from a Greek word meaning "a spark." Finally, we must beware of the many synthetic spinels which are sold under various names, including synthetic sapphire and aquamarine. Spinel Gemstone Buying Guide at DDB They may be distinguished by a good magnifier and also by ultraviolet rays. By these rays, the Natural Red Spinels appear a distinct red and the blue synthetics show an intense red tint. Synthetic blue sapphires give a violet tint, and the natural blue sapphires show hardly any glow. Spinel Gemstone Buying Guide at DDB Synthetic spinels will, of course, show single refraction and they seldom contain the curved lines and gas bubbles so characteristic of synthetic sapphires.
Spinel Gemstone for Jewelries
Since the particular group of Spinels Used in Jewelry Furnishes Stones which are often very attractive in color. They are sometimes called precious spinels, and almost every shade is known to exist. Spinel Gemstone Buying Guide at DDB Their wide range of colors may be compared to the fancy colored sapphires, colorless specimens being somewhat rare. Many intermediate shades are seen, and all are due to different metallic oxides. The color may be sometimes improved by careful heating. Spinel Gemstone Buying Guide at DDB The coloring agent in blue spinels, for instance, is iron. In these spinels, sometimes All the varieties crystallize in the same system (cubic) and the chemical constituents are analogous although the actual composition differs. Spinel Gemstone Buying Guide at DDB The natural crystals occur commonly as octahedra, which are often twinned. Chemically, spinel is a double oxide of magnesium and aluminum.
Aluminate, are among the several minerals which are classed within the spinel group, but the characteristic gem spinel, which excludes these minerals, is of a brilliant color and clearly transparent, especially in artificial light. Spinel Gemstone Buying Guide at DDB Although not common, it is found in a variety of colors, and it is often confused with other stones when cut and polished.calledgahnoThe orange-red stones are occasionally called rubicelles, the sapphire blue are naturally called Sapphire Spinels, the Different names are sometimes applied to various spinels, depending on their color, but such names are fortunately falling into disuse. They are really misleading; the simple term spinel is quite sufficient. The most usual colors seen are the ruby red and the rose red. Spinel Gemstone Buying Guide at DDB The former, known as ruby spinel, and the latter, known as balas ruby, are both attractive. These shades are the most expensive to-day, but as they are of small value compared with the ruby, they make a good substitute where a large red stone is required.
Spinels, zinc sometimes replaces the magnesium, particularly in specimens which come from Ceylon. Spinel Gemstone Buying Guide at DDB For that reason, the refractive index and the specific gravity will be found to be slightly higher than normal.
