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MINERAL SAND |
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Most sand on the beach consists of grains of the mineral quartz (SiO2). Mineral sands are old beach sands that contain concentrations of the important minerals, rutile, ilmenite, zircon and monazite. These minerals are heavy and are also called ‘heavy minerals’.
The relative density of common sand minerals such as quartz is around 2.65. The heavy minerals found in mineral sands have a relative density of between 4 and 5.5.
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Formation of Mineral Sand |
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Rutile, ilmenite, zircon and monazite originally grew as crystals in igneous rocks such as granite, pegmatite and basalt and some metamorphic rocks.
Over millions of years, these igneous and metamorphic rocks were weathered and eroded, and the grains of quartz and other minerals in the rock, including rutile, ilmenite, zircon and monazite, were washed down to the sea by heavy rainfall and fast flowing streams.
The heavy minerals were then carried back up onto the beach by waves. As the waves washed up and down on the beach, they carried the lighter quartz grains with them back into the sea, leaving the grains of the heavy minerals rutile, ilmenite, zircon and monazite behind on the beach . Wind also helped to concentrate the heavy minerals by blowing away the lighter quartz sand. These processes were repeated many times over millions of years, eventually creating a large deposit of mineral sands on the beach.
As the sea level rose and fell over geological time, the shoreline moved further inland and then back again. As this happened, the deposits of mineral sand were covered by more sand and built up or eroded and redeposited elsewhere. This is why we sometimes find mineral sand deposits many kilometres inland and maybe as much as 50 metres below the surface.
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ILMENITE |
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Ilmenite is named after the Ilmenski mountains in Russia, where the mineral was first discovered. Ilmenite is slightly magnetic, which means that magnets can be used to separate it from other minerals in mineral sands. It is able to withstand extreme temperatures, and is used in the steel industry to line blast furnaces. Ilmenite’s hardness also makes it useful as an abrasive.
Ilmenite is the main source of titanium dioxide which is used in paints, fabrics, plastics, paper, sunscreen, food and cosmetics.
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| Ilmenite |
| Chemical Formula: |
FeTiO3 |
| Colour: |
black/grey |
| Hardness: |
5-6.5 |
| Relative density: |
4-5 |
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MONAZITE |
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Monazite is named after the Greek word monazit, which means ‘to be alone’, because when it was first discovered it was thought to be quite rare. Monazite contains the elements: cerium, lanthanum, and neodymium, (known as the “rare earth” elements) and it is a rich source of the radioactive element thorium. Rare earth elements are used in high performance magnets, as pigment in ceramics, in robot motors, x-ray screens, fibre optics, energy efficient lanthanum lamps and colour television tubes. Thorium is radioactive and is used in incandescent gas mantles and in fuel for nuclear reactors.
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| Monazite |
| Chemical Formula: |
(Ce, La, Nd, Th) PO4 |
| Colour: |
brownish red |
| Hardness: |
5-5.5 |
| Relative density: |
4.9-5.5 |
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RUTILE |
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Rutile is named after the Latin word rutilus, meaning red. Rutile is a rich source of titanium dioxide. Titanium dioxide is a very white, opaque substance. Because of its opaque and reflective properties it is used as a pigment in paints, plastics and paper. Titanium dioxide is also used in sunscreen because of its ability to reflect UV light. Titanium metal is very strong and stable. It is used in spacecraft, guided missiles, jewellery, artificial joints and heart pacemakers.
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| Rutile |
| Chemical Formula: |
TiO2 |
| Colour: |
brownish red |
| Hardness: |
6-6.5 |
| Relative density: |
4.2-4.3 |
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ZIRCON |
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Zircon is named after the Arabic word Zargun, (derived from the Persian words: zar meaning gold and gun meaning colour). However, zircon can be a variety of colours: white, orange, yellow, yellowish brown, purplish red, light red, blue and green, and sometimes it is colourless. Some zircon crystals are of gemstone quality. Zircon’s hardness makes it useful as an abrasive. The melting point of zircon is over 2500° C, so it is used in the steel industry to line blast furnaces. Because zircon products are resistant to corrosion and heat, they are used in engines, electronics, spacecraft and the ceramics industry. Zircon products are also used in computer disc drives, for lightweight warmth and protection in clothing, and in many domestic products such as ballpoint pens and wear-resistant knives.
Zircon contains the metal zirconium, which is extremely hard and resistant to corrosion. Zirconium is used in nuclear reactors and chemical processing plants.
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| Zircon |
| Chemical Formula: |
ZrSiO4 |
| Colour: |
many |
| Hardness: |
7.5-8 |
| Relative density: |
3.9-4.8 |
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Mineral Sand in India |
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India has over 7,000 kms coast-line and many favourable stretches of the beaches on both the western and eastern shorelines have large reserves of heavy minerals whose potential is yet to be fully exploited.
Beach Sand contains the important heavy minerals such as Titanium bearing minerals including Ilmenite, Rutile and Leucoxene, as well as Zircon, Monazite, Garnet and Sillimanite.
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