Opal

  

Opal is a mineraloid gel which is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl and basalt. The word opal comes from the Latin opalus, by Greek ὀπάλλιοςopallios.

The water content is usually between three and ten percent, but can be as high as twenty percent. Opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common. These color variations are a function of growth size into the red and infraredwavelengths. Opal is Australia's national gemstone.

In the Middle Ages, opal was considered a stone that could provide great luck because it was believed to possess all the virtues of each gemstone whose color was represented in the color spectrum of the opal. It was also said to confer the power of invisibility if wrapped in a fresh bay leaf and held in the hand. Following the publication of Sir Walter Scott's Anne of Geierstein in 1829, however, opal acquired a less auspicious reputation. In Scott's novel, the Baroness of Arnheim wears an opal talisman with supernatural powers. When a drop of holy water falls on the talisman, the opal turns into a colorless stone and the Baroness dies soon thereafter. Due to the popularity of Scott's novel, people began to associate opals with bad luck and death. Even as recently as the beginning of the 20th century, it was believed that when a Russian saw an opal among other goods offered for sale, he or she should not buy anything more since the opal was believed to embody the evil eye.

Opal is considered the birthstone for people born in October or under the sign of Libra.