Spinel is one of the three birthstones of August, along with peridot and sardonyx. Spinel is a rare gemstone that often appears flawless and comes in a range of beautiful colours. It is also the fourth most durable gemstone with a rating of 8 on the Mohs scale, which comes just behind sapphire, ruby and diamond.
Spinel Origin and Formation
Like ruby and sapphire, spinel was formed under immense pressure and intense heat under the earth’s surface for millions of years. Moreover, it is usually found in the same areas, which explains why they are often confused with each other.
Spinels consist of magnesium, aluminum and oxygen atoms which turn into liquid when hot magma emerges from below the earth’s surface and seeps into cracks in igneous or metamorphic rocks. When the liquid cools, it turns into colourless crystals. However, this rarely happens in nature as magnesium aluminum oxide mixes with impurities and gets different colours.
It is worth mentioning that spinel is most commonly mined in alluvial deposits, meaning before being discovered and collected, spinel has been eroded from the rock in which it formed.
Spinels can be found in India, Pakistan, Afghanistan, Myanmar (Burma), Tanzania, Sri Lanka, Australia, Russia and Vietnam.
The wide colour range of spinels is caused by impurities or miniscule traces of other minerals mixed during its birth and growth process. If the microelement is chromium, the spinel turns red, pink or orange. In the case of iron, we get deep red colour spinels that look very similar to rubies. Blue, purple, violet, grey and black colours are caused by various combinations of manganese and cobalt microelements. Yellow and green spinel is extremely rare in nature, but it can be easily created in labs, so be wary when you see such colours in shops.
The most popular colour in spinels is ruby red, which is sometimes referred to as “traffic light red”. However, as naturally blue gemstones are rare, cobalt blue is also among the most sought-after spinel colours. Neon pink spinels from Mahenge, Tanzania, are also one of the most desired gemstones due to their amazing natural colour.
The colour changing phenomenon can also be seen in spinels. One type is bluish-grey in daylight and light purple under artificial light, other varieties turn from pink to lilac and blue to purple.
To figure out which spinel colour is the best, we need to consider the tonal grade and saturation of the stone. Tone refers to the level of lightness or darkness of the colour. It is graded from very light to very dark, where medium-tone spinels are the most valuable. Saturation refers to the intensity of the colour. This characteristic defines if the gem has weak, vivid, strong or intense colouring. For example, some red spinels may look brownish, while blue, purple and violet gems may look greyish. Spinels with strong saturation have the most beautiful deep colouring.
Spinel Clarity and Cut
Natural spinels can be transparent, translucent or opaque. However, in some cases, all three can be seen in one gemstone.
Even rough natural spinels are very transparent, which allows for seeing blemishes and inclusions. The clearer the gem, the better. However, distinctive fingerprint-like inclusions may add to the gemstone’s charm.
Since spinel is a durable gemstone, it can be cut and faceted into almost any shape, but cutters need to take special care to enhance the brilliance and maximize scintillation. It is a rare and valuable gemstone, meaning spinel can also be cut into a non-standard shape and size to minimize the rough yield.
The price of natural spinels is determined by their colour, clarity, cut and size.
Since deep red and cobalt blue spinels are the most popular, they command the highest prices. Pink, violet, orange, grey and black varieties can be found at much more reasonable prices.
In general, spinels with no inclusions or flaws visible to the naked eye are more valuable than those with obvious impurities. Although, the gems with the star effect caused by inclusions can be rather attractive. Larger spinels over 5 carats in any colour other than black are very rare, meaning they are very expensive.
Spinel Care and Cleaning
Spinel is a durable semi-precious gemstone, 8 on the Mohs hardness scale, meaning it is hard enough to survive accidental hits. However, you may want to take special care to prevent such abuse. It is always recommended to remove your spinel jewellery before household cleaning, playing sports, exercising or gardening.
To clean spinel at home, you use some mild dishwashing soap and warm water. Stir the water and dish soap together using a spoon or your finger. Carefully place your gemstones in the liquid and soak them for about 10 – 15 minutes. After the soaking, use a soft toothbrush to remove the dirt. Next, rinse out your piece of jewellery with clean water and dry it with a soft and lint-free cloth.
When storing spinel jewellery, keep it separated from other softer gemstones to protect them from being scratched. Similarly, you will want to protect your spinels from harder gemstones such as diamonds, sapphires and rubies, meaning it is a good idea to store spinel jewellery in individual cloth bags.
|Chemical Name||Magnesium aluminium oxide|
|Colours||Red, yellow, orange, brown, blue, violet, purple, pink, green, black, grey, colourless|
|Hardness||8 on the Mohs scale|
|Refractive Index||1.71 - 1.73|
|Specific Gravity||3.54 ~ 3.63|
|Transparency||Transparent to opaque|
|Fluorescence||Red spinel - strong red, blue spinel - weak reddish and green|
Featured image: Luen Wantisud / Canva