Sapphire crystal

Sapphire crystal is a very hard transparent material commonly used for "scratch-proof" watch glasses.

Made by crystallizing aluminum oxide at very high temperatures, it is chemically the same as natural sapphire and ruby, but without the small amounts of other elements such as iron, titanium or chromium that give the gemstones their colors. Sapphire (whether natural or synthetic) is one of the hardest substances, measuring 9 on the Mohs scale, a system for rating the relative scratch hardness of materials. (Diamond measures 10, the highest rating, and the hardest steels are 8).

Recently some high-end cellphones and PDA models have screens of sapphire crystal [cite web |url=http://science.slashdot.org/article.pl?sid=07/12/25/1539252 |title= The LCD Panel vs. The Crossbow |accessdate=2007-12-27 |author=timothy |date= |work= |publisher=] .

Synthetic sapphire is difficult, but not impossible, to scratch. In particular both diamonds and man-made materials that incorporate silicon carbide are harder than sapphire.

References