Opal – Birthstone for October
Opal is the birthstone for the month of October, along with pink tourmaline. It is also the stone given to celebrate the 14th year of marriage. The name opal is thought to be derived from the Sanskrit upala, meaning “precious stone,” and later the Greek derivative “Opallios,” meaning “to see a change of color.”
Opal as “…a mineral….that is a hydrated amorphous silica softer and less dense than 
quartz and typically with definite and often marked iridescent play of colors.” The opal is a stone so distinctive that everyone can identify it, with its many colored flashing lights. The brilliance and vibrant colors within an opal resemble the colors of fall, so it is an appropriate birthstone for the month of October. Opal is unique among gems, as it displays an array of very brilliant miniature rainbow iridescent effects, all mixed together.
The play of color comes from opal’s formation process, which is different than many gems. The color comes from the reflection of the scattering of light from the minute, uniformly sized and closely packed silica spheres that make up precious opal. The arrangement of these spheres, which vary in size and pattern, is responsible for the different colors. The more brilliant the color, or fire, the more valuable the gem. The most familiar opals are nearly opaque white or more translucent white, some having a black or reddish background. All opals vary greatly in their color of fire. Some have only red and orange lights, some also have green, and some also have yellow and blue lights. Black opals may have all of these colors as well as purple. Opals show just about every shade of every color in a variety of combinations. Opals with an abundance of red are usually the most expensive. Those strong in blue and green are equally as beautiful, but less rare, so their price is somewhat less. One of the most rare opals is called the Harlequin opal, which displays color patterns resembling a checkerboard.
