Blue sapphires have been used to make the most beautiful, high end jewellery for many years and have often been worn by royalty.
Blue sapphire is a gemstone variety of the oxide mineral, corundum, comprising of the two elements, aluminium and oxygen. These two chemical elements are required to form sapphire crystals. Blue sapphire can range in colour from very pale to very dark blue and it occurs when the sapphire crystals contain small amounts of iron and/or titanium, which act as a colouring agent.
Blue Sapphire Properties:
Refractive Index - 1.762 to 1.778
Birefringence - .008
Dispersion - .018
Optic Character - Uniaxial
Optic Sign - Negative
Specific Gravity - 4.00
Hardness - 9
Cleavage - Poor
Fracture - Conchoidal to Uneven
Lustre - Vitreous to Sub-adamantine
Transparency - Transparent to Opaque
Sapphires are crystals of the mineral corundum, made up mostly of atoms of aluminium and oxygen in a 2 to 3 ratio (Al203). The chemical bonds of aluminium and oxygen are particularly tight, making sapphire one of the hardest minerals known with a rating of 9 out of 10 on the Mohs Scale of Hardness. Sapphire is second only to diamond in hardness.
Corundum crystallizes in the trigonal crystal system and is typically found in three common shapes (habits); spindle-shaped bipyramids, columnar hexagonal prisms and tabular prism and rhombohedron combinations although a myriad of habit combinations are possible depending on the locality and colour. The crystals can take a range of forms, including bipyramidal, barrel and pinacoidal.
Sapphires come in a wide range of colours. The trace elements that cause the colouration in sapphire are usually iron (Fe) and titanium (Ti). Sometime vanadium (V) can also be present. If corundum is red then we call it ruby, which owes its colour to the trace element, chromium (Cr).
Sapphire and ruby are resistant to heat, light and chemicals.
Corundum from Sri Lanka can include crystals of zircon, rutile (silk fingerprint) and also, garnet, mica, pyrite, ilmenite, kyanite and diaspore.
Sometimes there is a ‘star’ effect (asterism) present in rubies and sapphires (which are polished in the cabochon style to show the effect to best advantage). Like cat's eye (chatoyancy), the effect is due to fine parallel fibres or crystals (usually rutile, but sometimes hematite).
The host rocks for sapphire are dolomotized limestone, marble, basalt and pegmatite. Ruby is formed in metamorphic dolomite marbles, gneiss and amphibolite. Rubies and sapphires are often mined from secondary alluvial deposits rather than from the primary rock, with the vast majority of sapphires and rubies (thought to be over 80%) being produced by artisanal and small-scale mining (ASM) operations.
Some of the most well-known sapphire producing countries are Sri Lanka (Ceylon), Madagascar (Ilakaka), Tanzania (Umba), USA (Montana) and Australia (Queensland). Historically, many impressive sapphires were discovered in Kashmir at the end of the 19th century, whilst Burma (Myanmar) produced some of the world's finest rubies for a long period. The current leading producer for ruby is Mozambique.
Natural rubies and sapphires often contain a profusion of microscopically small canals or crystals, known as ‘silk’ that reflect the light and produce a whitish sheen, thereby detracting from the beauty of the gem material. Typically these crystals consists of rutile (titanium oxide).
Therefore a large percentage (some people quote up to 90%) of corundum is heat treated to improve the colour and clarity. This can be a very simple, relatively low temperature treatment using traditional blowpipe or other basic techniques. It could also be a gas or electric furnace with temperatures going as high as 1800C or more. The melting point for corundum is just over 2000C.
By heating the stones steadily and progressively through increasing temperatures over a period of hours or even days, it is possible to improve the overall clarity of rubies through the partial or complete dissolution of the rutile needles or intensify the colour of blue sapphires as the titanium is slowly diffused into the stone. This technique was used extensively and with great effect by gem traders from Thailand, who converted seemingly worthless "geuda" corundum from Sri Lanka into fine blue sapphires during the 1960s.
Of course, there is always a chance that heating can cause the sapphire to crack or explode and, for that reason, heat treatment is usually performed on rough material rather than faceted.
After heat treatment, it is sometimes possible to see the so-called "snowball", "cotton ball" or "halo" effects caused by crystal inclusions or trapped gas bubbles expanding during the heating process. Whilst these can indicate possible heat treatment, they should not be considered as conclusive evidence.
Blue sapphires are very popular in United Kingdom, not least because of the connection with the British royal family.
Sapphire is the birthstone for September.
On the Mohs Scale of Hardness, sapphire (corundum) is rated as a 9 (as is ruby, which is also corundum), making it second only to diamond in terms of its resistance to scratching. This is one of the reasons why it is a popular choice in jewellery that is worn regularly, such as engagement rings.
The vast majority of blue sapphires on the market today have been heat-treated in some way to improve their colour and clarity. Heat treatment in a gas or electric furnace is now a standard procedure in the gem industry.
Sapphire can also demonstrate different shades of blue/purple in natural or artificial light. These beautiful stones are called “colour-change” sapphire.
Cornflower Blue Sapphire, 1.29ct, cushion cut
Some of the best blue sapphire in the world has originated in Ceylon (Sri Lanka) and Kashmir. The term “Kashmir Sapphire” is often applied to outstanding examples of this gemstone, even when the stone itself did not come from that region.
Ceylon / Sri Lanka has been an important source of blue sapphires for many centuries. Even today, the gemstones are mined by hand from gravel deposits that cover large parts of the southern half of the country. Blue sapphire from Sri Lanka comes in a range of stunning colours, but they are typically light-to-medium blue. Some of the largest Sri Lankan cut gemstones, such as the Logan Sapphire, weigh up to several hundred carats.
Blue Sapphire, 2.62ct, rough crystal
Sapphire can also be found in a number of other locations around the world including Madagascar, USA, Myanmar, Australia and Thailand.
Blue sapphire is the birthstone for people born in September.
Blue Sapphire, 1.59ct, pear cut
Throughout history, sapphire has been a symbol of truth, sincerity and faithfulness in relationships. It is said to bring peace, joy and wisdom to the wearer and owner. In the past, the sapphire was also believed to be a talisman that would give protection against evil spirits. Sapphires are also said to represent “divine favour” they have traditionally been a favourite gemstone for kings and queens. For example, the British Crown jewels contain many blue sapphires, including the Stuart Sapphire and the octagonal St.Edward's Sapphire.
As we mine some of our own sapphires in Sri Lanka, we discover a wide range of blue sapphire, no gemstone is ever the same. Here is sample of the blue sapphires we have mined in the past. If you have specific requirements for gemstones then please let us know.
Blue Sapphire, 1.19ct, round cut
Blue Sapphire, 1.75ct, oval cut
Blue Sapphire, 3.40ct, oval cut
Blue Sapphire, 2.09ct, oval cut
Blue Sapphire, 2.27ct, oval cut
Blue Sapphire, 1.75ct, cushion cut
Please get in touch with your blue sapphire requirements via our contact page. If you want to read more about the amazing blue sapphire, please see this page from the Gemological Institute of America - Blue Sapphire from the GIA