History & Introduction

Opal is the October birthstone. Opal gets its name from various languages: in Sanskrit upala, meaning "precious stone", in Latin it is called opalus and in Greek it is known as opallios, both meaning to see the change in color. The most interesting characteristics of opal is the capacity to reflect as well as refract to a specific wavelengths of light. Different wavelengths of light interplay and provides opal a unique visual appeal, and create it one of the most desirable gemstones in the world. It is one of the world's most beautiful and precious gemstone to be known.

The earliest known opal artifacts was discovered back from 4000 BC that came from Ethiopia. These artifacts were discovered later in a cave in Kenya by famous archaeologist, Louis Leakey. In the middle Ages, opal was taken as the 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 even known to confer the power of invisibility if wrapped in a fresh bay leaf and held in the hand. In novel of Scott, the Baroness of Arnheim wears an opal talisman that possess supernatural powers. On the talisman, when a drop of holy water falls, the stone becomes colorless and thus soon the Baroness dies. With this people began to connect opals as bad luck and death. This dropped the sale of opals in Europe in 1829 by 50%, and continued to be low for the next twenty years or so.

Recognise - The concentration of opal is hydrated silicon dioxide that contains from three to thirty percent water. The following feature along with its relative softness with a rating of 5.5 to 6.5 makes opal quite easy to recognize and discern from other gemstones. Not like the other gems with play of color or iridescent effects, opal even shows 'opalescence'. Additional lustrous stones don’t show this pearl-like bluish color effect that appears to glide across opal, however in fact it will mainly display color, which will appear abruptly, disappear and then reappear, it depends upon the viewing angle. In large number of cases, close observance of color and optical phenomena can usually help distinguish opal from many alike gemstones.

Availability - Gem Opal from Brazil, Polished opal from Yowah, Queensland, Australia, Multi-Color solid black opal cabochon from Lightning Ridge, NSW, and Australia produces around 97% of the world's opal. Coober Pedy in South Australia is considered to be the primary source of opal.

Usages - Opal is one of the most precious gemstones, in which Black Opal is the most valuable and desired form whereas White Opal and Precious Fire Opal even is available expensive in the market. Opals gemstones are cut then polished into cabochons, and in a few cases they are faceted into several cuts. Opal is one of the popular stones among mineral collectors and museums compete to get the finest specimens. There is no industrial or commercial use for Common Opal, except for those specimens that are brightly fluorescent and are collected by fluorescent mineral collectors.

Buying Guide

Color - Opal is available in various colors, which includes white, colorless, pale yellow, pale red, grey, brown and black. Diffraction can cause flashes of any color of the rainbow which can be seen in opal's color play. Yellow, blue and green are commonly found colors whereas violet, red and orange are rare and they are seen through play of color. Opalescence mainly comes in milky blue in color, however it available in fewer colors. The saturation of the color of the body, the play of color as well as the transparency determine an opal's value.

Clarity and Lustre - Opal gemstones are also available in transparent to opaque. Materials that are from transparent to translucent are naturally more valuable as compared to opaque materials. Mainly, all opal will have some visible internal fractures or inclusions such as patches, potch (common opal) or matrix rock inclusions. Opal tends to exhibit a wax to resinous luster which helps accentuate play of color and opalescence. Stone that are fine as well as have a vitreous luster.

Cut and Shape - Opals are usually cut into shapes which maximize and preserve the weight of the rough opal. They are often cut en cabochon and depending on the opal color bar, it may be cut as per high or low domes in order to maximize play of color and adularescence. Opal can also be faceted and is mainly seen with 'fire opal'. Opals can be found in various shapes, including traditional ovals, rounds and cushions, as well as fancy hearts. Opal is often carved into ornaments.

Treatment - Though opal is typically untreated, however it is impregnated with wax, oil or even plastic to improve the color along with stability. It may also be layered (as in doublets or triplets) in case of durability. Treatments method of 'Smoking' currently are more common as before. The method of 'Smoking' is done to darken the color of the body. There are forms of synthesized opal available. Technically they are 'imitation opal' as they often include substances such as plastic that are not found in natural opal.

Gemological Characteristics:

Chemical Formula	SiO2_nH2O - Hydrous silicon dioxide
Color	White, grey, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black.
Transparency	It varies in optical density from opaque to semi-transparent.
Crystal Structure	Amorphous; kidney or grape-shaped aggregates
Hardness	5.5 to 6.5
Refractive Index	1.37 to 1.52
Density	1.98 to 2.50
Cleavage	None
Composition	Hydrous silicon dioxide. The water can range from 3% to 21% of the total weight, but is usually from 6% to 10%.
Streak	White
Double Refraction or Birefringence	None
Lustre	Waxy to resinous
Fluorescence	White opal: white, bluish, brownish, and greenish; fire opal: greenish to brown
Specific Gravity	1.98 - 2.25
Fracture	Conchoidal
Tenacity	Brittle
Other ID Marks	1) Rich play of color in some specimens. 2) Often fluoresces, usually bright green; but also light green, light blue, purple, and white.
In Group	Silicates; Tectosilicates; Silica Group
Rock Type	Igneous, Sedimentary, Metamorphic
Popularity (1-4)	1
Prevalence (1-3)	1
Demand (1-3)	1

Classification:

• Pink opal
• White opal
• Black opal
• Yellow
• Orange
• Red
• Purple Opal
• Blue Opal
• Green Opal
• Grey Opal
• Brown Opal
• Black Opal
• Cat’s eye Opal
• Opal Doublet