OPAL (Hydrated Silica Glass)

	OPAL

Chemistry: SiO₂ - nH₂O; Hydrated Silicon Dioxide.
Class: Mineraloids
Group: Some minerologists place Opal in the Quartz Group.
Uses: As a gemstone and ornamental stone.
The Physical Properties of Opal
For natural opal mineral specimens see our For Sale or Sold lists
For Opal Jewelry, see --> OPAL JEWELRY

Opal has been a popular gem for many centuries and has a very interesting structure. Opal is considered a mineraloid because this structure is not truly crystalline. The chemistry of Opal is primarily SiO₂ and varying amounts of water. The amount of water varies from 5% to 10% and sometimes greater. This water can help geologists determine the temperature of the host rock at the time the opal formed.

Although there is no crystal structure, (meaning a regular arrangement of atoms) opal does possess a structure nonetheless. Random chains of silicon and oxygen are packed into extraordinarily tiny spheres. These spheres in most Opals are irregular in size and inconsistent in concentration. Yet in Precious Opal, the variety used most often in jewelry, there are many organized pockets of the spheres. These pockets contain spheres of approximately equal size and have a regular concentration, or structure, of the spheres. This has the effect of diffracting light at various wavelengths, creating colors. Each pocket produces a different color and with a different intensity, depending on the angle from which a viewer sees it. The multicolored flashes of light that Opal emits gives it a truly beautiful and valuable look. This effect is called a "play of light", and not "opalescence". The latter term describes the milky nature of the translucence of opal, and is more properly compared to the appearance of water to which a few drops of milk have been added.

The name opal probably is derived from the Sanskrit name for precious stone; upala. It has been mined for centuries, at least since Roman times when they extracted the opal from areas now within the Czech Republic. The Aztecs made use of local Mexican sources as did the Spaniards when they exported the material back to Europe. Today most precious opal comes from Australia with significant sources from Mexico and the Western United States.

Not all opal is so precious however. Common opal lacks opalescence, color or luster and is . . . after all . . . common. Opal is often imitated, forged and "enhanced". Fluorescence, while somewhat unreliable is a good method to determine authenticity.

Opal is the modern Birthstone for October.

PHYSICAL CHARACTERISTICS:

Color is white, colorless, pale yellow, pale red, gray or black when impurities are common. Diffraction can cause flashes of any color of the rainbow (play of light).
Luster is vitreous to pearly.
Transparency: Specimens are transparent to translucent (opalescent).
Crystal System: Does not apply because opal is amorphous.
Habits include massive, cavity-fillings such as in fractures and geodes, nodular, reniform or as a replacement of other minerals and wood.
Cleavage is absent.
Fracture is conchoidal.
Hardness is 5.5 - 6
Specific Gravity is approximately 2 - 2.5 (light)
Streak is white.
Other Characteristics: Most specimens will fluoresce white or pale green, some phosphoresce and all specimens can be very sensitive to impacts and low temperatures.
Associated rocks are chert (a form of microcrystalline quartz), volcanic rocks and many others.
Notable Occurrences include many Western USA localities; Mexico; Australia; England; Czech Republic and many other localities around the world.
Best Field Indicators are color play & opalescence, low density, fluorescence, fracture filling tendency and lack of cleavage or crystal faces.

Amethyst Galleries sells natural opal specimens. For Fine Jewelry, see our affiliates:

Opal Jewelry - Hover over an item for more information

Australian Opal Ring with Tanzanite
Metal:ÿSilver .925Size:ÿAll sizes are available. If not we resize them for free of charge.Metal Finish:ÿRhodiumStone/s:ÿAustralian Opal + Tanzanite + CZÿThis item usually arrives in 2-3 business days. Arrival date depends on the item selected.Shipping...Only $192.40 at

Australian Opal Ring with Tanzanite
$192.40
Silver Best Buy

Tanzanite and Inlayed Opal Ring
Beautiful Tanzanite and Inlayed Opal Ring. Fine quality silver opal ring from SilverBestBuy Co.Metal:ÿ14K Gold Plated over Silver .925Size:ÿAll sizes are available. If not we resize them for free of charge.\nMetal Finish:ÿRhodium 14k Gold...Only $261.04 at

Tanzanite and Inlayed Opal Ring
$261.04
Silver Best Buy

Sterling Silver Rainbow Fire Australian Black Opal Triplet (Boulder Opal) Ring Jewelry
This Ring was handmade by a master artisan and is one of a kind.Only $161.99 at

Sterling Silver Rainbow Fire Australian Black Opal Triplet (Boulder Opal) Ring Jewelry
$161.99
JeGem.com

Pink Opal Birthstone Necklace in Sterling Silver
This sterling silver necklace features a beautiful, bezel-set pink opal and an engravable circle tag. The necklace measures 20 inches in length, and can be fastened at 18 or 19 inches for added versatility. Engrave the circular disc with any initial...Only $65.00 at

Pink Opal Birthstone Necklace in Sterling Silver
$65.00
Blue Nile

Mexican Fire Cherry Opal Silver Ring
Marquise Cut Mexican Fire Cherry Opal Silver Ring with approximately 10 carat fire cherry opal made with .925 sterling silver and a rhodium finish to give it a white gold look.Metal:ÿSilver .925\nSize:ÿAll sizes are available. If not we resize them for...Only $259.74 at

Mexican Fire Cherry Opal Silver Ring
$259.74
Silver Best Buy

Heart-Shaped Pink Opal & Diamond Pendant
Sweetly romantic, this heart-shaped pink opal and diamond pendant goes from denim to dressy. Metal: Sterling silver Metal Color: Rose Stones: Heart-shaped pink opal Other Stones: 1/10 ct. t.w. round diamonds Closure: Spring-ring Length: 18 cable chain...Only $185.00 at

Heart-Shaped Pink Opal & Diamond Pendant
$185.00
jcpenney

Sterling Silver Fire Cherry Opal Ring
Pear cut Fire Cherry Opal about 3 carat stone Silver Ring made with .925 sterling silver and a rhodium finish to give it a white gold look.Metal:ÿSilver .925\nSize:ÿAll sizes are available. If not we resize them for free of charge.\nMetal...Only $186.94 at

Sterling Silver Fire Cherry Opal Ring
$186.94
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3 Round Cut Fire Cherry Opal Ring
3 Round Cut Fire Cherry Opal Ring with approximately 4 carat fire cherry opal made with .925 sterling silver and a rhodium finish to give it a white gold look.Metal:ÿSilver .925\nSize:ÿAll sizes are available. If not we resize them for free of...Only $181.74 at

3 Round Cut Fire Cherry Opal Ring
$181.74
Silver Best Buy

Australian Opal Ring with Pink Sapphire
Metal:ÿSilver .925Size:ÿAll sizes are available. If not we resize them for free of charge.Metal Finish:ÿRhodiumStone/s:ÿAustralian Opal + Pink Sapphire + CZÿThis item usually arrives in 2-3 business days. Arrival date depends on the item...Only $183.04 at

Australian Opal Ring with Pink Sapphire
$183.04
Silver Best Buy

Australian Opal Ring with Smoked Quartz
Metal:ÿSilver .925Size:ÿAll sizes are available. If not we resize them for free of charge.Metal Finish:ÿRhodiumStone/s:ÿAustralian Opal + Smoked Quartz + CZÿThis item usually arrives in 2-3 business days. Arrival date depends on the item...Only $181.74 at

Australian Opal Ring with Smoked Quartz
$181.74
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Blue Lab-Created Opal Inlaid Omega Back Pierced Earrings In Sterling Silver by PalmBeach Jewelry
Rated by 25,000+ Customers. Blue Lab-Created Opal Inlaid Omega Back Pierced Earrings In Sterling SilverOnly $55.99 at

Blue Lab-Created Opal Inlaid Omega Back Pierced Earrings In Sterling Silver by PalmBeach Jewelry
$55.99
PalmBeachJewelry

Lab-Created Opal & White Sapphire Necklace at JCPenney
appraised at learn more about appraisals Always a crowd pleaser, this elegantly styled necklace features beautiful opal with white sapphire complements. Metal: 14K gold over sterling silver Metal Color: Yellow Stones: 2.7 ctw. lab-created opal, 9x6mm,...Only $100.00 at

Lab-Created Opal & White Sapphire Necklace at JCPenney
$100.00

14K Gold Over Sterling Opal Drop Earrings at JCPenney
appraised at learn more about appraisals These gold earrings lend calming style to your look with cool opal stones as their main focus. Metal: 14K gold over sterling silver Metal Color: Yellow Stones: 8x5mm, 6x3mm lab-created opal Other stones: 1.5mm...Only $75.00 at

14K Gold Over Sterling Opal Drop Earrings at JCPenney
$75.00

Opal, Tourmaline & Sapphire Ring In 14K Gold Over at JCPenney
Two pink tourmalines and a swirl of white sapphires flank a large, milky opal on a ring a fairytale princess - or you - could own. Metal: 14K gold over sterling silver Metal Color: Yellow Stone: .5 ctw. oval genuine multicolor opal, 8x6mm Other Stones:...Only $75.00 at

Opal, Tourmaline & Sapphire Ring In 14K Gold Over at JCPenney
$75.00

Cherry Opal Necklace
Metal:ÿSilver .925Size:ÿ22 mm x 12 mmMetal Finish:ÿRhodiumStone/s:ÿFire Cherry OpalÿShipping Information:This item usually arrives in 2-3 business days. Arrival date depends on the item selected.Shipping via FedEx Express Worldwide.ÿOnly $119.60 at

Cherry Opal Necklace
$119.60
Silver Best Buy

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