How does sapphires form

The purest and most translucent forms of corundum are created by recrystallization of minerals during the metamorphosis of rocks that are of igneous origin. It is a process that takes millions of years and only a few places in the world have rock outcrops where these rare crystals are exposed by weathering. The pure form of the mineral corundum is clear and colorless, but mineral 'impurities' that seep into the Aluminum Oxide as the rock cools give it its fabulous colors.

The distinctive colors of many gemstones are caused by the presence of transition metals as impurities in an otherwise transparent crystal lattice. The best rubies, however, are found in marbles, particularly at mines in Myanmar Burma but also in Vietnam, Afghanistan, Pakistan as well as Nepal. The most famous deposits of corundum-sapphires ever to be found, are from deposits in Kashmir, Burma and Sri Lanka Ceylon in the illustration above you can see how India has pushed along into the Asian continent.

Below is a crystal of rough corundum you can see how corundum comes in many different colors and depending on what was naturally present millions of years ago gives each stone is unique color and beauty. Allow Cookies. Home How Sapphires Are Formed? These then become concentrated in certain parts of the landscape after being transported by rivers and streams placer deposits. Most of the sapphires and rubies from eastern Australia occur in placer deposits. Ruby deposits are more uncommon as they depend on the presence of the rare element chromium.

Ruby is usually found in metamorphic rocks, such as those in the Harts Range in the Northern Territory. However, a more transparent, gemstone-quality ruby comes from a few areas in eastern Australia where it has been brought up from underlying metamorphic rocks by volcanic action. Marc Antoine Gaudin synthesised the first rubies by fusing alumina with chromium in Ten years later Jacques- Joseph Ebelmen made artificial sapphires by fusing alumina with boric acid.

Auguste Verneuil developed a process for producing large flawless sapphires and rubies in These crystals have many industrial uses including as mechanical bearings, as laser components, and in optics.

Sapphires and rubies have been found in all eastern Australian states, including Tasmania. The Kings Plains area, near Inverell, has some of the richest deposits of gem-quality sapphires ever mined.

In addition, sapphires have been recovered from old tin workings along the Weld River in Tasmania. There are many sites where fossickers can try and find sapphires and rubies in these regions too. The most significant occurrence of ruby is near Gloucester, near Mount Barrington, an old volcano.

Rubies have also been found in the vicinity of the Macquarie and Cudgegong Rivers and near Tumbarumba. See map. Currently commercial mining of corundum including sapphire and ruby still occurs at the Anakie and Lava Plains placer deposits in Queensland, and the New England area of New South Wales. Open pit mining is used to extract the corundum ore from the gravels.

In many cases the mining operations are small and the pits quite shallow. Tools used might include jack hammers, excavators or shovels.

Some countries in Africa and South America use high water pressure mining to produce large quantities of rough corundum gems. However, many gem buyers boycott companies using this practice, because this method strips away all the top soil destroying the local environment. Once mined, corundum can be separated from clay and gravel because it is more dense and heavy. Usually, the gravel is broken up and sorted into size fractions in a rotating drum trammel , and then washed either by hand or with a high pressure water jet, over filters with various size holes.

The heavy grains will sink and the lighter materials, like clay, will wash over the top. The remaining material also contains other heavy minerals such as magnetite and zircon. Magnets can be used to get rid of magnetic material and then zircons are removed by hand.

The corundum is then visually assessed and graded according to size and colour. From its use in Chinese axes dating back to around B. But not all sapphires are blue; the colors we see are the result of impurities and a process called charge transfer.

Corundum crystals of gemstone quality in any color other than red are called sapphires, while red varieties are called rubies. These are among the most brilliant and hard gemstones; only diamonds are harder. The intense blue of the sapphire is caused by the addition of titanium and iron to the mineral corundum. Sapphires are described by their colors blue, green, and yellow , with the most sought-after color being cornflower blue.

The color is very stable, even when exposed to light and heat. Both rubies and sapphires owe their intense colors to impurities, ruby to the presence of chromium, and blue sapphire to both titanium and iron. In rubies , the color can be explained by crystal field theory, but in sapphire, a slightly different process, known as charge transfer, produces the color blue.

Although sapphires are found in various parts of the world, not all regions produce the colors that are highly valued. For example, Australia is a dominant producer of sapphires, but these stones are considered less valuable due to their very dark color.

Fine quality sapphires are produced in Southeast Asia, with those from Sri Lanka often having the sought-after cornflower blue color. Corundum that contains a few hundredths of one percent of titanium is colorless.