The different types of opals
The noble opal is whitish, milky, semi-transparent and clearly shows the irization phenomenon, now uniform, now by dots and stripes. The drapes are often pearl gray or blue, but can also be colored.
Harlequin opal, for example, has numerous macules packed together, like the proverbial patches that make up the Bergamo mask dress; the flame has a striped iridescence; the one known as sunflower shows blue and gold reflections. The most important noble opal deposits are found in the Czech Republic, Germany, Mexico, England and Australia.
Black opal has a black ground color and can be opaque with some translucency, especially when exposed to an intense light source. Gray opal is a rarely used name: specimens of this variety are usually included in the “Black” or “Dark” category, but are distinguished by a translucent to opaque gray body. Its composition is as follows: SiO2 + H2O + C, Fe (carbon and iron), color: black, iridescent.
White opal, also called “Opal Chiaro“, is a very popular and fashionable gem. It can be translucent or opaque with a white body. White opal is characterized by a milky opaque background and the colors can be very bright and vivid. In the classification of opals, the white tone is identified by N9. The mines located around the mining town of Coober Pedy, in the state of South Australia, are the primary source for this valuable opal.
Welo Opal has an electric neon color and different patterns on a predominantly white body, although some specimens are yellow or amber. Welo opal is found in quartz veins at a depth of 2 to 3 meters below the surface. The difficulty of its extraction is mainly due to the methods used. This stone was discovered in the mountainous region “Semien Wollo” in northeastern Ethiopia.
It is distinguished by its bright and shiny color and its wonderful transparency. Welo opal also enchants with its changing reflections that show all the rainbow colors, especially yellow, orange, red and green. Welo opal can be composed of water up to 8% of its weight. And another interesting aspect is that the hardness of the opal is on the Mohs scale between the values of 5.5 and 6.5. Therefore, a Welo opal should not be approached or worn with quartz or other harder stones, such as beryl, corundum and diamond. Your Welo opal could be scratched by the harder stones.
Gelatin opal can be transparent or translucent and, due to the absence of the parent rock or without background color, or if it is positive, it is called “Crystal Opal”, “White Crystal Opal”, “Dark Crystal Opal” or “Black Crystal Opal”. Opals that are opaque with a matrix (host rock) included in the cut are called pebble opals; each opal with a visible host rock in front is called “Opals with matrix”.
But not all opals have a color scheme. Fire Opal is a transparent or translucent opal crystal with no interplay of color, where instead it shows wonderful shades of orange, red, yellow and even blue or brown.
The red and green reflections remind in this type the warmth of the flame. It is generally found in eruptive or sedimentary rocks, or in secondary deposits produced by the erosion of the latter, especially in Australia. Fire opal is even more beautiful than the noble and sensitive to external influences: air, light, temperature, water. Subjected to these, tends to crack and become milky, losing the beautiful reflections that are its most prominent feature. The most common form, for this stone, is the curved cut surface; the fire variety, however, can also be multiform with a satisfactory aesthetic result. Buriti fire opal is mined in Brazil and enchants with its red and orange colors, reminiscent of Mexican fire opal.
Boulder opal, from Queensland, is characterized by different shapes and colors on smooth or blunt surfaces. The opal in this case is found as a coating on a rock matrix. Peruvian Opal is a rare variety that has beautiful translucent blues, pinks and greens, without color schemes. Another variety without color scheme is the translucent yellow and green opal from Tanzania.