All About Rutile in Gemstones
Rutile is a substance that makes frequent appearances in the gemstone world. Rutile is responsible for the "silk" that makes some rubies and sapphires especially valuable. It is also the cause of most asterism (the star effect) and chatoyancy (the cat's eye effect). It is microscopic inclusions of rutile that create these unusual optical phenomena. Rutile becomes visible in the inclusions characteristic of rutilated quartz, where large rutile needles form fascinating and unique patterns.
But what exactly is rutile? Where does it come from? Can you buy gemstones made entirely from rutile?
Rutile is a mineral composed primarily of titanium dioxide. Its refractive index is among the highest of any known mineral, at 2.616 to 2.903. Diamond, by contrast, has a refractive index of 2.417 to 2.419. Natural rutile varies in color and can be golden, blood red, reddish-brown or black, with the color resulting from the presence of iron (sometimes up to 10%). It has a density or specific gravity of 4.20 to 4.30 and a hardness rating of 6 to 6.5 on the Mohs scale.
The most important rutile deposits are in Sierra Leone in West Africa where 30% of the world's supply is located. Other deposits are found in Minas Gerais, Brazil, the Swiss Alps and Arkansas in the USA.
Natural rutile is rarely found as a gemstone (it is mostly seen as inclusions in other gems) and is classified as a collector's stone.
Synthetic rutile was first produced in 1948, by a special variation of the Verneuil method, using extra oxygen. The high refractive index gives an adamantine luster and strong refraction that leads to a diamond-like appearance.
Synthetic rutile was sold as a diamond simulant in the 1950s, under names such as Titania. However, because rutile is not especially hard, it was eventually replaced by more durable diamond simulants.
Rutile has some important industrial applications. Finely powdered rutile produces a brilliant white pigment that is used in paint, plastic, paper, food, and other materials that call for a bright white color. Titanium dioxide is also a key ingredient in many sunscreen products. Nanoscale particles of rutile are transparent to visible light but are highly effective in the absorption of UV light. So sunscreens made with titanium dioxide can protect against UV induced skin damage.
- Primera publicación: Octubre-24-2008
- Última actualización: Enero-23-2019
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