Sapphire

The gemstone sapphire is a variety of an aluminium oxide and the mineral corundum, although trace amounts of various other elements such as magnesium, copper, chromium, titanium, and iron give it different colours that include green, orange, purple, yellow and corundum blue. Blue is the traditional colour for sapphire despite it being found in many other colours. A red sapphire is known as a ruby. A sapphire can also have a mixture of colours that are then known as bi-coloured, rainbow, or parti sapphires.

Sapphire is a durable product that is the second hardest substance to be found in nature. Diamond is the only gem that is harder. The hardness of sapphire is partly due to its short, strong, aluminium- oxygen bonds. These bonds pull the aluminium and oxygen atoms together that cause it to be quite dense and hard.

It is generally accepted that sapphire is a valuable gemstone used as a jewel for decorative purposes although it is also used in the following applications:
- As an infra-red optical component used in scientific instruments
- High durability glass
- Crystals for tiny movement bearings in wristwatches
- Extremely thin electronic wafers such as that required in integrated circuits
- Titanium sapphire lasers
- Bar-code scanners used in stores

Mining for sapphire has taken place in Australia for more than 100 years and commercial mining of sapphire for 50 years. The quality of Australian sapphire has been consistently high throughout this period although it has not received the appropriate recognition for such a performance. This has been mainly attributable to it being marketed by international vested interests as 'Thai' and 'Ceylon' sapphires. As a result Thailand, Sri Lanka and Burma are regarded as countries producing quality sapphire for the world market whereas commercial deposits of sapphire in these countries actually became depleted many years ago. Madagascar and Australia are, in fact, the real source of sapphire sold today under these countries names.

The production of synthetic sapphire has grown in recent years as it can be made by industry from agglomerated aluminium oxide, fused and sintered in an inert hot isostatic pressing atmosphere. This process yields a transparent polycrystalline sapphire that is slightly porous. A more traditional method of producing synthetic sapphire is carried out using a Czochralski, Verneuil, flux method that creates a single crystal sapphire product that is not porous. Early in the 2000's, world production of synthetic sapphire reached 250 tonnes that was mainly used in Russia and the United States. Cheap synthetic sapphire gave industry unprecedented use of what was previously a rare material.

One of the first reported finds of sapphire in Australia occurred in 1851 when it was discovered by gold miners along the Macquarie and Cudgegong rivers in NSW. Three years later a discovery was made in the New England area of NSW and in 1875 sapphire was found at Retreat Creek in Queensland. These discoveries were mostly alluvial being found along former watercourses. This led to the belief that sapphire was formed deep in the crust of the Earth and brought to the surface by volcanic action. This accounts for most Australian sapphire deposits being associated with basalt. It appears sapphire was eventually eroded from the basalt and became concentrated in ancient river systems and streams.