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Opal, Sphene And Andalusite

Opal is a mineraloid gel which is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl and basalt. The water content is usually between three and ten percent, but can be as high as twenty percent. Opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common. These colour variations are a function of growth size into the red and infrared wavelengths. Because opals are as individual as a fingerprint, they make a romantic gift. Napoleon gave Josephine a beautiful opal with brilliant red flashes called "The Burning of Troy," making her his Helen. Opal is softer than many other gems and should be stored carefully to avoid being scratched by other jewellery. It should also be protected from blows, as exposed corners can chip. Opal should not be exposed to heat or acid. To clean, wipe opal with a soft cloth

Sphene is named from the Greek word for wedge, because of its typical wedge shaped crystal habit. It is also alternatively called titanite for its titanium content. Sphene can be cut as gems although it is considered a rarity on the gem market. It brings to the table a fire greater than diamond and unique colour shades. However its softness limits its desirability as a gemstone. Twinning is common in sphene and forms a classic twin shape that is found mostly in Pakistan. The twin is shaped like a deflated, caved-in football, only with flatter surfaces. Sphene can form nice crystals and can make a lovely addition to the collection of a collector who appreciates different crystal forms

Andalusite is named after Andalusia, the province of Spain where it was first discovered. Andalusite is pleochroic, i.e. it shows different colours in different directions. When cutting most pleochroic gemstones, such as iolite and tanzanite, the trick is to minimise the pleochroism and maximise the single best colour. With andalusite the opposite applies: cutters try to orient the gem to get a pleasing mix of colours: orange-brown and a yellowish green or gold. When they succeed, andalusite looks quite unlike any other gemstone, with patterns of colour dancing around the facets. The best colour play is seen in fancy shapes, particularly rectangular cushion shapes: in round cuts, the colours blend together. Andalusite is mined in Brazil and Sri Lanka.

 

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