Some Australian examples of these gems can be seen at Google Arts and Culture - Gems from the Safe. Gemstones that were referred to as semi-precious are used in jewellery and ornaments. Diamonds, rubies, sapphires, and emeralds were originally considered the ‘precious stones’, but sometimes this category included opal, jade, or pearls. However, these divisions are not scientific and have never been truly meaningful. In the mid-1800s, gemstones were first classified as either ’precious’ or ‘semi-precious’. Precious, semi-precious or ornamental stones
A two carat diamond is larger than a two carat cubic zirconia and very much more expensive. This means that cubic zirconium is heavier than diamond. For example, diamond has a specific gravity of 3.52 and a cubic zirconia, which looks very similar, has a specific gravity of 5.80. Most gemstones are harder than quartz (Mohs scale greater than 7) and cannot be scratched by the blade of a knife. Using properties of minerals such as habit, shape, lustre, light refraction and specific gravity we can tell the difference between similar looking gemstones. The test of a good gemstone is its resistance to wear and tear. Information on some of Australia's gemstones can be found at Google Arts and Culture - Gems from the Safe. Australia is the world’s biggest producer of diamonds and opals and major supplier of sapphire, ruby, emerald, garnet, topaz and jade has also been mined in Australia. Australia, with its long geological history, has some of the world’s oldest rocks and minerals and a wide variety of gemstones.
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