12. September 2016 05:54 /
In recent times, Andalusite gemstones have risen in prominence in the semi-precious gem market. Known for its enchanting beauty and polymorphic appearance, buying an Andalusite is a highly revered option for brides and newly engaged couples who wish to look beyond the usual collection of rubies, garnet, emeralds and sapphires.
Here are some enticing facts about the Andalusite gemstone.
Andalusite is basically an aluminium mineral gemstone belonging to the families of zircons. Being a neo-silicate gemstone, it is relatively hard and can be scratched only by diamond and corundum drills. Andalusite gemstone is a trimorphic compound, meaning that it is found in the nature in three different physical forms. Other two forms are Kyanite and Sillimanite.
It is a deep blue silicate gemstone found in metamorphic and sedimentary rocks. Other names of kyanite are disthene, rhaeticite and cyanite. It is used as abrasive item, in addition to being used as an insulator. Its major application as an Index Mineral to measure depth, temperature and pressure of metamorphic activity is specially utilized in mineralogy and mining.
Sillimanite is named after its discoverer, Benajmin Silliman, an American chemist. It was first studied in 1824, and occurs as fibrolite in twisted fibre form in metamorphic and sedimentary rocks.
Sillimanite is largely used in glass industry and reinforcement material manufacturing industry.
Andalusite and its colouring effects:
Andalusite exhibits pleochrosim with distinct combination of vibrant colours. It is mainly due to the small concentration of impurities like Manganese and Iron that manage to dope into Aluminium octahedral structure. One of the varieties of Andalusite is the Viridine, that basically has huge levels of Iron and Manganese.
High level of Manganese is revealed through its pink and whitish red or grey colour. Darker the colour, higher is the concentration of Manganese in the structure.
How to identify Andalusite:
Andalusite shares its lineage with many gemstones in the neo-silicate and beryl families. It is quite possible that even best of gemstone collectors get confused while buying Andalusite. It is commonly mixed up with sphene, smoky quartz beads, tourmaline gemstone and idocrase.
One of the distinguishing factors to identify Andalusite is its pleochroism. It exhibits a special type of pleochroic effect known as Trichroic effect, meaning that a ray of light gets split into three sections after passing the crystal.
Some gemstone collectors identify a pure Andalusite from its colour consistency and clarity. They are usually found in yellow, green and olive colours. It is common to find Andalusite in the dual colour shade, mostly in different intensities. Cutters often minimize the pleochroism by cutting the gemstone in oval, pear and marquise cuts to exemplify one particular colour.
Some natural Andalusite gemstones are translucent with dark inclusions in the form of wires and veins. They are called “Cross Stones”. They are not purely Andalusite, and sold in the market as Chiastolite.
Pure Andalusite is hardly exposed to any heat treatment procedures. However, Chaistolite is heat treated or filled with resin to improve clarity and pass off as a pure Andalusite. Pink Andalusite are derived by treating dark green-brown gemstones , but this is mostly reversible.
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