Sapphire is an aluminum oxide, which crystallizes in the trigonal system. The stone's hardness is 9 on the Moh's scale. It has a refractive index of 1.762-1.77 and a 3.97 - 4.05 specific gravity.

Sapphire and ruby are members of the corundum family, a group of crystallized aluminum oxides. Both have exactly the same chemical composition and only small amounts of colouring trace elements distinguish between them.
Sapphire appears in all possible colors except red, such as blue, yellow, green, purple, pink and brown. The term Sapphire, when used on its own, refers only to the blue variety of sapphires, which ranges from very strongly greenish Blue to Blue to bluish Violet, while sapphires in all other colours (also known as ‘Fancy sapphires’) occupy the rest of the entire spectrum and are named together with their associated colour prefix, such as ‘orange sapphire’, ‘pink sapphire’, ‘green sapphire’ etc. In the purple to red region, which is also associated with Ruby colours, a gem with low saturation of purple-red will be defined as ‘Pink Sapphire’ or ‘Purple Sapphire’ (according to the tone).
 

Sapphire ring

Sapphire is the birthstone for the month of September and the gemstone representing the fifth and 45th wedding anniversaries.

It was believed that sapphires could influence spirits and reveal the secrets of oracles. They were deemed to attract wealth, bring harmony between lovers, make peace between enemies and protect the wearer from envy and infidelity. They were also thought to strengthen the well-being and overall health of the owner, clear the mind and skin, cure fevers, colds, eye diseases and ulcers and were used as an antidote to poison. Sapphire is a long-time symbol and guardian of purity and it represents truth, sincerity, and consistency. Sapphire is mentioned in the Bible as one of the gemstones on the High Priest's breastplate.

Among the blues, two colours are considered to be the most sought after – ‘Royal Blue’, the most desired and most valued shade within the trade, and ‘Cornflower Blue’, resembling the colour of the famous flower.

Pink sapphire is typically found in colours of a bright, delicate pink to a pink with a slight tinge of violet. It is considered to be the highest valued fancy coloured sapphire. The border between pink sapphire and ruby is vague and differs between different markets around the world.

Purple sapphire colours range from violetish Purple, which is designated a ‘Violet Sapphire’, to Red-Purple, which is identified as ‘purple sapphire’. Yellow sapphire ranges in colour from pale to canary yellow, gold, honey, and brownish yellow and is found in quite large quantities. The lighter and brighter colours are the most common, whereas golden yellow gemstones of high quality are very rare and command high prices. Yellow sapphires with another noticeable secondary hue, such as green, grey or brown or orange tint, are more common.

Pure orange sapphires are very rare and very popular among collectors. Most of the orange sapphires display a yellow, red or brown tint. Light Pink-Orange coloured sapphires from Sri-Lanka are called ‘Padparadscha sapphire’, named after the padparadscha lotus flower. This gemstone is very beautiful and rare, and currently is in great demand by collectors. There are African sapphires which have an orange-red colour reminiscent of the valuable padparadscha sapphires of Sri Lanka, albeit possessing a more brownish tint. These gems are termed African padparadscha.

Green sapphire colours range from Yellow-Green to Blue-Green, where the majority displays bluish Green colours with a metallic greyish tint.

Sapphire has many sources worldwide:

Sapphires from Kashmir are known for their beautiful velvety-blue, slightly milky colour, similar to that of the cornflower. The mine area is in Zanskar, near the city of Soomjam in India. Gems said to originate from this source fetched extremely high prices – much higher than the prices given for Sri Lankan or even Myanmar sapphires of similar quality.

Myanmar is considered to be the world's second-most precious source for blue-coloured sapphires. The two main sources are Mogok and Mong-Hsu. The colour of the Myanmar sapphire is violetish Blue and it is commonly referred to as ‘Royal Blue’.

The main sources of Thai sapphires are Kanchanaburi and Chantaburi. Thai sapphires are very dark blue (‘Navy Blue’) to almost black in colour and can be classified into a number of colour-types: Common Thai, Bankacha colour and Kanjanburi colour.

Corundum is found in many areas of Sri Lanka and in an astounding variety of colours, including the much-coveted padparadscha sapphires. The blue sapphire's colour is generally weaker than the colours of the Myanmar variety. Since the early 1970s, sapphires from Sri Lanka have been heated according to a number of undisclosed methods, thereby improving their colour. Today it is considered as the 3rd most prestigious source (after Kashmir and Myanmar).

Pailin, Cambodia, is a well-known source of fine blue sapphires. Cambodian sapphires tend to display rich saturated blue to violetish Blue colour with an attractive lustre.
 

Fancy sapphire bracelet

Madagascar is the world leader in sapphire production since 2007, after the discovery of enormous sapphire deposits in Ilakaka in 1998. Ilakaka and Andranandambo are the major areas for sapphires in Madagascar. Madagascar sapphires tend to present a highly-saturated, milky-apparent, violetish Blue colour. Due to their resemblance, they are frequently confused with Kashmir and Sri-Lankan sapphires but their prices are much lower.

The Umba River and the Morogoro area in Tanzania are sources of fine sapphires in a wide range of colours. The Songea region is another source that produces sapphires with metallic Violet-Blue colours, with a noticeable greyish or greenish tint. The Songea gemstones are usually small and most of them have very strong pleochroism.

Australia is an important supplier of rough sapphires, mined mainly in New South Wales and Queensland and for years provided the majority of the cut merchandise in the market. Most of the small, cheap sapphires polished in Thailand are of Australian origin. Australian blue sapphires commonly display a slight greenish or greyish hue, a result of the heating process applied to most of the dark Australian merchandise to lighten the material and improve its clarity, and also possess distinct zoning characteristics.

Montana sapphires display fine pastel Violet-Blue colours but also greyish Green, Green and Yellow to colourless hues. Pink to red gemstones are rarely found. The Montana gemstones are not homogeneous in colour, are fairly included and generally have very strong zoning. The sizes of the rough extracted from the mine are small, rarely yielding gemstones above one carat.

Additional sources around the world include Vietnam, Laos, Kenya, Zimbabwe and Nigeria.