Lexi Webster
Australia is home to several extensive deposits of garnets, which are found in a variety of locations across the country. The Australian landscape provides an ideal geological setting for the formation and extraction of these precious gems, with significant deposits located in Western Australia, New South Wales, and the Northern Territory. The garnets found in Australia exhibit an array of physical characteristics, including diverse colour variations and unique chemical compositions, making them appealing both aesthetically and scientifically.
| Characteristics | Values |
|---|---|
| Colour | Red, orange, yellow, green, purple, brown, blue, black, pink or colourless |
| Composition | Complex silicate minerals with a similar chemical formula, physical properties and a common crystal system |
| Crystal formation | Individual crystals, pebbles or clumps |
| Transparency | Opaque to transparent |
| Size | Up to one meter in diameter |
| Geological setting | Igneous rocks |
| Locations | Port Gregory, Broken Hill, Harts Range, New England, New South Wales, Northern Territory, Spotted Tiger campground, Mount Hope, Newry Station |
| Uses | Jewellery, ornaments, sandblasting, abrasive wheels, sandpaper, polishing grits and powders, water filtration |
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What You'll Learn
The chemical composition of Australian garnets
Garnets are a group of complex silicate minerals with a similar chemical formula, similar physical properties, and a common crystal system. The chemical composition of garnets varies, resulting in a range of hardness on the Mohs scale of about 6.0 to 7.5. The harder species, like Almandine, are often used for abrasive purposes.
There are six main types of garnets, each with a distinct chemical composition that influences its features such as colour, density, and hardness. These types are Almandine, Pyrope, Spessartine, Grossular, Andradite, and Uvarovite. The first five are used as gemstones, while the last one is more exotic.
Almandine, also known as Oriental garnet or almandine ruby, is iron-rich and occurs in metamorphic rocks like mica schists. Pyrope, derived from the Greek word "pyrōpós" meaning firelike, is red in colour and chemically an aluminium silicate with the formula Mg3Al2(SiO4)3. The magnesium in Pyrope can be replaced in part by calcium and ferrous iron. The colour of pyrope varies from deep red to black, with a violet-red variety called rhodolite. Spessartine is a manganese garnet coloured from orange to red, with fine crystals found at Broken Hill, New South Wales. Grossular garnet is found in the Harts Range of the Northern Territory, occurring in its pure, colourless form, and with iron added to create yellow, orange, and red shades. The yellow and orange colours are known as hessonite garnets.
Garnets can also be classified as lithium-oxide garnets, which have gained interest from researchers for their use as electrolytes in batteries. Additionally, yttrium aluminium garnet (YAG), with the formula Y3Al2(AlO4)3, is used for synthetic gemstones and lasers.
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The geological setting of Australia
The geology of Australia is extremely diverse, spanning almost all known rock types and a geological time period of over 3.8 billion years. This includes some of the oldest rocks on Earth, dating back 4.4 billion years.
Australia is a continent situated on the Indo-Australian plate. Its geology can be divided into several main sections: the Archaean cratonic shields, Proterozoic fold belts and sedimentary basins, Phanerozoic sedimentary basins, and Phanerozoic metamorphic and igneous rocks.
The Archaean cratonic shields include the Yilgarn, Pilbara, and Gawler cratons, which are among the oldest parts of the Australian continent. These cratons are flanked by Proterozoic orogenic belts and sedimentary basins, such as the Musgrave Block and the Arunta Block.
The Proterozoic fold belts, such as the Amadeus Transverse Zone in central Australia, guided the overthrusting of blocks and the formation of the continental margin during seafloor spreading in the Mesozoic era. The Phanerozoic sedimentary basins include the Glengarry Basin and the Bangemall Basin, while the Phanerozoic metamorphic and igneous rocks are found in the eastern part of the country.
Australia has been part of all major supercontinents, including Pangaea and Gondwana. It finally separated from Gondwana (the African continent and Indian subcontinent) in the Cretaceous period, around 84 million years ago. This separation gave rise to the unique geological setting of the Australian continent, which has continued to evolve through intraplate earthquakes and the stress of plate boundaries.
The mineral wealth of Australia, including garnets, has played a significant role in its history and economy. The garnets found in Australia exhibit a wide range of colours and physical characteristics, making them valuable for both ornamental and industrial purposes.
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Locations of garnet deposits in Australia
Australia is home to several extensive garnet deposits. The country's landscape provides an ideal geological setting for the formation and extraction of various types of garnets.
The largest garnet mine in the world is located in Port Gregory, Western Australia. The mine, known as the Port Gregory Garnet Mine or GMA Garnet Mine, was discovered in the late 1970s and opened in 1983. The garnets at this deposit were transported to the site by streams and rivers from a nearby area of very old garnet-rich metamorphic rocks. The garnets from this mine are used for industrial purposes, such as sand blasting and water jet cleaning applications, rather than as gemstones due to their small size.
Another significant source of garnets in Australia is Broken Hill in New South Wales. Fine crystals occur at this site, and garnets have been extracted from the area since the 1880s as a by-product of mining other minerals from metamorphic rocks. The Thackaringa district near Broken Hill also has extensive areas of garnet-bearing metamorphic rocks and mines that have operated intermittently since the 1960s.
Garnets can also be found in the Harts Ranges in the Northern Territory. Grossular garnet, which can be found in its pure, colourless form and with the addition of iron to give it a yellow, orange, or red colour, is present in this region. The yellow and orange garnets are known as hessonite garnets. A deposit of garnet was discovered in this area in 2010, but garnets have been extracted from the Harts Ranges since the 1880s.
In Queensland, Mount Garnet has deposits of red and green garnets. Gem-quality garnets can be found near Proston, Mount Tarampa, and Mount Wyangapinni. Additionally, garnets can be found in the Bathurst to Orange district of New South Wales.
For those interested in searching for garnets themselves, the Spotted Tiger campground, located 125 km northeast of Alice Springs, is a designated fossicking area.
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Industrial uses of garnets
Australia is home to several extensive deposits of garnets, with significant deposits located in Western Australia, Port Gregory, Broken Hill, and Harts Ranges. While garnets are often thought of as gemstones, most garnet mining is for industrial uses. The industrial applications of garnets include:
Abrasives
The majority of garnet mining is for massive garnet that is crushed and used to make abrasives. Garnet is a relatively hard mineral, with a hardness that ranges between 6.5 and 7.5 on the Mohs scale. This allows it to be used as an effective abrasive in many types of manufacturing. When crushed, garnet breaks into angular pieces that provide sharp edges for cutting and sanding. Garnet sandpaper, made from crushed garnet granules, is widely used in woodworking shops. Garnet is also used to make sanding belts, discs, and strips.
Water Jet Cutting
Garnet is used in water jet cutting, a process where a machine produces a high-pressure jet of water with entrained abrasive granules. When these are directed at a piece of metal, ceramic, or stone, it produces a cutting action that generates very little dust and cuts at a low temperature. Water jet cutters are used in manufacturing and mining.
Water Filtration
Garnet is used in water filtration processes.
Blasting
Garnet is used as a blasting material, particularly in abrasive blasting.
Polishing
Garnet is used for precision grinding and polishing.
Indicator Mineral
Garnet is also used as an indicator mineral during mineral exploration and geologic assessments. Pyrope-rich garnet, for example, is used as an indicator mineral in the search for diamonds.
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Historical significance of garnets
Garnets have been captivating humans for thousands of years, with the earliest recorded use of garnets being traced back to ancient Egypt. In ancient times, these precious stones were revered for their unique qualities and rich colours. They were used in jewellery and as decorative accents in royal tombs. Egyptians believed that garnets had protective properties and wore them as amulets to ward off evil spirits.
The allure of garnets extended beyond Egypt, with ancient civilisations such as the Greeks and Romans also recognising their beauty and symbolism. The deep red hue of garnets was associated with passion, love, and courage, making them highly sought-after. Greek mythology mentions garnets as being associated with the goddess of love, Aphrodite, further enhancing their desirability. During the Roman Empire, garnets were used in intricate jewellery pieces, signet rings, and as inlays in various decorative items.
Garnets continued to hold significance during the medieval period in Europe, with people believing that dragons had eyes made of garnets. They have also been associated with heart, blood, inner fire, and life force. The word garnet comes from the 14th-century Middle English word "gernet", meaning "dark red". It is borrowed from Old French "grenate" from Latin "granatus", possibly referring to "pomegranate".
Even in modern times, garnets remain treasured gemstones, often used in engagement rings, earrings, and other forms of jewellery. They are valued for their metaphysical properties, believed to provide strength, balance, and protection to the wearer. Garnets are also used for industrial applications such as abrasive blasting and water jet cutting, showcasing their versatility beyond their aesthetic appeal.
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Frequently asked questions
Yes, garnets are found in Australia. The country is home to several extensive deposits of these precious gems.
You can find garnets in Western Australia at Port Gregory, Broken Hill, Harts Range, and the New England area in New South Wales.
Australian garnets exhibit a wide range of colours due to their chemical compositions. They can be red, orange, yellow, green, purple, brown, blue, black, pink, or colourless. They also vary in transparency levels and crystal formations.
