Opal

Opal is the birthstone for October (along with Tourmaline) and the anniversary gem for the 14th year of marriage. Opals in large sizes are rare and costly, especially black opal. Usually cut as cabochons, sometimes beads. Occasionally found as fossilized (opalized) clamshells, snail shells, or wood. Transparent opals, such as Mexican red or orange fire opal, are often faceted. Values are normally determined by the presence and nature of color flashes (play of color). Opal's scratch hardness is measured at 6.0 to 6.5 on the Mohs' scale.