|All About Rutile
Rutile is a substance that makes frequent appearances in the gemstone world. You will encounter rutile in connection with the "silk" that makes some rubies and sapphires especially valuable. You'll find it again in connection with 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. It has a refractive index among the highest of any known mineral, with a value of 2.616-2.903. Diamond, by contrast, has a refractive index of 2.417-2.419. Natural rutile varies in color from golden to blood red, reddish brown and black, with the color resulting from the presence of iron (sometimes up to 10%). It has a density or specific gravity of 4.20-4.30 and a hardness rating of 6-6.5 on the Mohs scale.
The most important rutile deposits are in Sierra Leone in west Africa with 30% of the world's supply. Other deposits are found in Minas Gerias, Brazil; in the Swiss Alps; and in Arkansas in the USA.
Natural rutile is rarely found in the market as a gemstone (as opposed to an inclusion in other gem species) and is classified as a collector's stone. Synthetic rutile was first produced in 1948, by means of a special variant 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 1950's, under names such as Titania. But because rutile is not especially hard, it was eventually replaced in the market by more durable diamond simulants.
Rutile has some important industrial applications. Finely powdered rutile produces a brilliant white pigment and is used in paints, plastics, papers, foods, and other applications 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.
- First Published: October-24-2008
- Last Updated: October-06-2010
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