The birthstone for the month of October is the beautiful opal. It is also the national gemstone of Australia, as 80% of all opals in the world are found in South Australia. The stone is deposited at lower temperatures, and can be found in sandstone, rhyolite, basalt, limonite and marl, although it can be found in the fissures of many other types of stones. It is considered to be a hydrated amorphous silica and mineraloid because it usually has approximately 8% water content.

[caption id="attachment_546" align="aligncenter" width="323"]Photo by Jessa Dow-Anderson (Flickr) Photo by Jessa Dow-Anderson (Flickr)[/caption]

The Formation of the Opal

The opal is produced as a result of the seasonal rains in the desert outback of Australia. As the rain seeps into the ground, it moves towards the rock that has developed underground. When this rainfall evaporates and dries up in the underground ancient sedimentary rock, it leaves behind deposits of silica. These deposits in the rocks are what form the opal in the stone. The deposits of color are called the opal's play-of-color.

The Different Types of Opals

There are precious opals and common opals. Precious opals display a vivid play-of-color, while common opals simply have less color. Opals can also be varied in their optic density. Some opals are opaque and others are semi-transparent and seem almost see-through. The internal structure of a precious opal diffracts light in a way that is like a grid and that makes the color easier to see. These opals can be white, clear, black, brown and all of the colors of the rainbow. Opals containing a red hue up against a black stone are the rarest, while the most common are green hues hidden in a white stone.

The Different Categories of Opals

There are five main categories of opals.

  • White Opal: The white opal is translucent to semi-translucent and the play-of-color is against a light background.
  • Black Opal: The black opal is translucent to opaque and the play-of-color is against a dark background.
  • Fire Opal: The fire opal is transparent to translucent and has red, orange, yellow or brown body color. It can also be called a Mexican opal.
  • Boulder Opal: The boulder opal is translucent to opaque and has a light to dark background with its play-of-color. Occasionally it can seem grayer in comparison to a black or white opal. It may also even include the surrounding rock as part of its beauty.
  • Crystal Opal: Also called the water opal, it is transparent to semitransparent with a background that is clear. The play-of-color on a crystal opal is very beautiful and is displayed very clearly.

The History of the Opal

Originally symbolizing love and hope during ancient Roman times, the opal was given the nickname "light of the world". In their language, the word for "precious stone" was synonymous with the word "opalus" because of its meaning and symbolization. They also compared the colors of the stones with the stars, fire, and volcanoes. In some ancient cultures, the people believed that there were supernatural powers in the opal. They believed that they stones had fallen from the sky through lightning bolts.

Greek cultures believed that the stone was protection from deadly diseases, while in Europe, it was considered to symbolize truth and purity. Throughout history, the opal is considered to be a lucky stone, bringing luck to those who wear it. The more the display of color within the stone, the luckier the wearer would be.

I believe that the opal is one of the most extraordinary stones in that it can be completely different depending on the display of color and the opaque to translucent appearance of each individual stone. It is truly an unusual and astounding gem to grace any type of setting for a beautiful piece of jewelry, regardless of when your birthday happens to be.