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Gemstones Facts

 

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SpinelSpinel Gemstone

Mohs scale hardness: 8

Spinel is one of the hardest minerals and a brilliant red gem that is found in some of the same locales as ruby. This has led to great confusion in gemstone history, as spinels have often been mistaken for rubies. In fact, some of the famous "rubies" in the British crown jewels are actually spinels, including the 170-carat Black Prince's Ruby set into the British Imperial State Crown and the Timur Ruby which is a 352 carat spinel engraved with the names of the some of the mogul emperors who previously owned it.

The source of both of these gems is believed to be Myanmar, where most significant spinels are mined. The Myanmarans recognized spinel as a separate gem species as early as 1587, but beyond its border, spinel was referred to as "balas ruby" for hundreds of years.

Spinel Crystal Structure and Properties

Spinel and ruby are chemically similar. Ruby is aluminum oxide and spinel is magnesium aluminum oxide. Spinel crystallises in the system of isometric, common forms of the crystal are octahedral, usually twinned. It has imperfect octahedral cleavage and a conchoidal fracture.

The spinel gemstone is clear, transparent and flawless. Small inclusions may also be seen after adequate magnification only. Since many spinel gems are almost devoid of flaws and clean, most of them found in the market are untreated.

Spinel is found primarily in metamorphic rock, and as a primary mineral in basic rock. Spinel is also found in igneous and carbonate rock. In molten rock or magma, the absense of alkalis (sodium hydroxide or calcium hydroxide) prevents the formation of feldspar. If alumunium oxide is present in the magma, corundum (ruby) wil form or the alumunium oxide will combine with magnesium to form spinel. Ruby and red-color spinel derive their coloration from the same chromium ion plus trace amounts of iron, manganese, and zinc. This is why spinel and ruby are often found imbedded in the same matrix.

Colors of Spinel

This gem is found in many different colors ranging from red, purple, pink, violet, indigo to blue and green. Pure spinel is white, but mineralogists believe that the orange to purplish stones owe their color to the trace elements and minerals like chromium and iron, while the natural pink and red spinel derive its color from trace element and mineral chromium. Initially, the spinel of natural blue was believed to owe its beautiful color to iron, however it has benn found to have traces of cobalt too. It is now believed that the lesser the amuont of iron present in the stone, the better the blue color. Blue spinel is also known as cobalt spinel.

Red spinel is the rarest and most valuable amongst the spinels, followed by the cobalt blue spinel. There is a unique natural white spinel which surfaced briefly in Sri Lanka, now lost. The transparent red spinels were called balas-rubies or spinel-rubies. In the past, before the arrival of modern science, rubies and spinels were equally known as rubies. They look identical and are found in the same localities. Today, distinctions can be made through hardness and x-ray tests. In fact, many famous old “rubies” were found to be spinel like the Black Prince’s Ruby from the royal crown of England and the Timur Ruby.

Types of Spinel

The blue to dark blue variety is called Gahnite, the violet variety is called Almandine Spinel, the ark green variety is called Gahnospinel, the brown variety is called Picotite, the dark red to black variety is called Galaxite, deep-red variety is known as Ruby Spinel, yellow to orange variety is called Rubicelle and the black variety is called Hercynite. There are also star spinels and color change spinel varieties but those are not easily found.

Spinell is a synonym of spinel, piconite is a synonym of picotite, pleonaste is also known as pleonast and flame spinel is a synonym of rubicelle.

The common simulants of the natural spinel are zircon, aquamarine, synthetic spinel, tourmaline, cobalt glass, ruby, sapphire and garnet. When purchasing spinel gems, make sure the spinel is not synthetic. Most colorless spinels sold in the market are synthetic, as are some red ones. Other ways to differentiate spinel from other gemstones is that spinel posesses no electrical properties when subjected to heat, yet the garnet and ruby do. Spinel has an amazingly high melting point of 2135 Celsius.

The name spinel is believed to come from the Greek word spinos, for spark. Spinel has been a long time favorite of the serious gem collector, due to its incredible brilliance, outstanding durability and wide array of colors. Making spinel even more attractive is its surprising affordability, often attributed to the general public's lack of awareness of the gemstone. For those looking for an alternative to higher priced rubies and sapphires, spinel may be the best choice.

Spinels are mined in Burma (Myanmar), Sri Lanka (previously called Ceylon), India, Afghanistan, Sweden, Brazil, Thailand, United States and Australia. The best spinels are found in the burmese mines (fine quality burmese rubies are also found in that mines).

It is believed spinels have special properties:

 

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