Chemical Composition: SiO2 nH2O Cleavage: None Color: Purple to blue, typically with a matrix matrix Crystal System: Amorphous Form/Habit: Massive Fracture: Conchoidal Gravity: 1.9-2.3 Hardness: 5-6 Luminescence: Green (long and short wave) Luster: Vitreous Streak: White Transparency: Translucent to opaque
Where does Opal come from?
Opals are found in many locations around the world, however 90% of all Opals on the market are Australian in origin. Other deposits are located in Czech Republic, Ethiopia, France, Honduras, Hungary, Italy, Madagascar, New Zealand, Peru, Portugal Slovakia, and the United States (Idaho and Nevada).
What is Opal?
Opal is a type of Common Opal and a Silicate mineral. Silicate minerals form the largest family of minerals, including more than 25% of all known minerals and 40% of all common minerals. In addition to being a major part of the Earth’s crust, Silicate minerals have also been found on the moon and in meteorites. Silicates are minerals which contain the elements Silicon (a light gray shiny metal) and Oxygen (a colorless gas). Together, these two elements form a tetrahedron – a shape similar to a pyramid – with a Silicon atom in the center and Oxygen atoms at each of the four corners. These tetrahedra connect with other chemical structures, in six different ways, to form various minerals and rocks. There are six main groups of Silicate minerals, and these main groups are further subdivided into secondary subdivisions, such as Quartz and Feldspars. Opal comes in two main varieties, precious and common. Precious Opals have a fiery play of colors sparking across their surface. Common Opals, by contrast, lack this fire and have an opaque, flat color.
Common Opals are fairly widespread and can be found in most types of rocks, wherever silica-bearing waters are found. Opals are especially abundant near hot-springs and Opal often is part of the fossilization process for Petrified Wood as well as fossilized seashells and bones. Precious Opals, by contrast, are much more rare and can only be found enclosed within a rock, where over time the water is slowly removed from the silica gel, a process which can take thousands of years. The silica left behind settles down and, if it settles in the correct formation, it results in the iridescent color which plays across the gem’s surface.
How is Opal mined?
Most Precious Opals are found in thin layers embedded in sandstone and are the primary focus for many mines. Some of the mines are small affairs, while others are huge operations that create vast tunnel systems through the sandstone. Precious Opals are found using UV lights. Common Opals, by contrast, are secondary stones found in a wide variety of mines and mining conditions.
Julie Abouzelof is the owner of Moonrise Crystals and an advocate for responsibly sourced gems and minerals. Her first career was in education teaching history, geology and anthropology, as well as working with special-needs students. She is now a heart-centered entrepreneur who encourages mindfulness and positive action to heal ourselves and the world. Julie lives in Hawaii with her lover and a little parrot named Darwin.