Corundum - a fantastic gemstone - better known to most in its gem form as Rubies and Sapphires. It is an incredibly hard stone and is found in every colour you can imagine. Only reds and very deep bluish pinks (almost reds) are called rubies. Every other shade, from colourless, through yellow, grey, green, pink, blue and purple - as well as many more - are called sapphires. Most people only associate blue with sapphire, but more recently the pinkish orange padparadscha and pink varieties have become really popular in the jewellery trade.
The mineral is the crystal form of Aluminium Oxide and the colours found are from tiny impurities of Chromium, which gives ruby its red colour, Titanium and Iron which give other sapphires their colours. It is formed in igneous and metamorphic rocks where it can grow into large crystals. The crystals are barrel shaped and the gem is part of the trigonal crystal system. Corundum can be found in many places, including Myanmar, Thailand, Australia, Africa and India where the stones have been mined for centuries. Many stones are not mined from the host rocks, but can be found in sands and gravels as they are resistant to erosion.
Some stones exhibit interesting and unusual optical properties, such as asterism. This can be seen as a six rayed (can be four, six, eight or twelve rays) star which runs across the surface of the stone under certain lighting conditions. Asterism is caused by dense inclusions of tiny, parallel fibres in the mineral which cause the light to reflect back as a star. This can best be seen in stones that have been cut en cabochon.
Many gems can be treated or enhanced in some way to improve colour and stability. There are many treatments from dying or coating stones - usually used for lower grade gems, to irradiating to intensify colour. Some are waxed, oiled, lead infused and so on. Many of these treatments are fully acceptable by the jewellery trade and do not devalue the stones. The best stones are naturally clear or transparent, with good, even colour saturation of good intensity with no or very few internal and external flaws or inclusions when seen under x10 magnification - really rare I have to tell you! Most stones of reasonable colour or clarity will demonstrate some colour zoning or visible crystal growth lines.
The gemstone is incredibly hard, with a hardness of 9 on Moh's scale of hardness, only being topped by diamond. This makes the stone a fantastic choice for rings or other jewellery as it is highly resistant to wear. Indeed, it will scratch almost all other gems. In industry, low grade stones are used as abrasives and for making some sandpapers!
Corundum is widely synthesised for industry and for jewellery making purposes. Even asterism can be replicated. If the stones look too good to be true and the stars too clear and definite, then it is most likely that the stones are not natural, although this isn't always the case of course. A good indicator would be the price of the stone and whether it is from a reputable dealer or not!
Lets have a look at some of these gorgeous stones in action, so to speak, in fantastic creations by Folksy artisans. Please click on the pictures to be taken to the items in the crafters shops.
This stunning bracelet by Sophie Wolchover features a large, opaque ruby as its focal point.
A fantastic and unique ring by Prooshan Blue featuring a large Indian Ruby
Stunning opaque ruby and gold filled wire, makes this necklace by Faith Bowman a real statement piece.
Superb Boss Style ruby earrings look like ancient treasures! By Deborah Jones
I adore this fun pendant! A pair of cherries make the perfect foil to these lovely rubies, by Stephanie Mann
A little ruby number from me - this one has quite a pinkish tone. It has been set as a pendant in sterling silver.
Gorgeous blue sapphires and pearls have been teamed together in these lovely earrings by Carol Smalley
A simple and elegant sapphire ring by Nicholas Guy, featuring the use of Eco-Silver.
Another simple ring design, this time featuring an orange sapphire and black oxidisation of the silver, by Hannah Morris-Knowles. She also has other rings with coloured sapphires, including pink, available in her shop.
Pretty studs with lovely sapphires in classic blue, by John Furness
A really unusual one of a kind piece, featuring an uncut orange sapphire, by Huiyi Tan
Colour graduated sapphires create a stunning necklace - this piece has been designed by Linda Runeckles
These are really different! Pink Corundum set into sterling silver and brass - they make a real statement. Earrings by John & Dawn Field
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I could go on for ever and a day about rubies, sapphires and corundum, but I feel I have done enough for anyone who might be interested to take the plunge and dive in for a closer look. I do hope you will!
Jacqueline x
