We are now almost halfway through November. Kind of shocking, isn’t it? 2011, you have flown by at far too brisk a pace.
Rutile is one of the natural forms that titanium dioxide (TiO2) takes. It is mined for use as a plain white pigment, and can be found in paint, toothpaste*, food coloring, sunscreen and as a coating for welding rods. Sierra Leone has one of the largest deposits of rutile in the world, and it is one of their largest exports.
That same ability to create free radicals that makes it (potentially) a good use in green infrastructure, has created some concern that it’s use in sunscreens could be harmful — with some groups suggesting that it might cause skin cancer rather than prevent it. The Australian government conducted a review of the scientific literature (PDF) in 2009, and found that those fears were unfounded. They concluded that TiO2 is only a danger if it comes in direct contact with viable skin cells while it is exposed to sunlight; and because most of our outer layer of skin is dead, the nanoparticles can’t reach the living cells to damage them.
Those are the useful uses of rutile, but it has another, more glamorous side as well. Rutile is found as an inclusion** inside of numerous gemstones, often with beautiful results. This might seem counterintuitive, as people typically want their gemstones to be clear. Rutile is the exception to that rule.
When included in rubies or sapphires, rutile can form beautiful star-like images under the surface, shining through the red or blue. Gems that have a star have to be cut into a cabochon instead of faceted — this means that instead of the typical clear, angular cuts favored for precious gems like diamonds, a gem with a star will be polished to have a smooth round top, like a dome, otherwise the star-like effect is lost entirely.
*Proof! Click the link and look under ingredients. Back
**Inclusion = Something within a rock, usually another mineral that is literally included in a gemstone. Used in a sentence: Needles of rutile included in quartz crystals are rutile inclusions. Geologists tend towards practicality when naming phenomena. Back