Boulder Opal

OPAL

Jelly Opal
Yowah Nut Opal Hyalite Precious Opal Opalite
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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
Round Sapphire Sterling Silver Ring with London Blue Topaz & Fire Opal - Venus Band
Scalloped shells form a fluted pattern on each side of this feminine tapered band, carefully handcrafted in your choice of gems and metals.Only $210.00 at Gemvara
no photoRound Sapphire Sterling Silver Ring with London Blue Topaz & Fire Opal - Venus Band
$210.00
Gemvara
Men's Round Peridot Sterling Silver Ring with Fire Opal - Octagon Ring
Eight-sided geometry frames a brilliant gemstone in this bold and striking man's ring inspired by the octagonal rotundas of neo-classical architecture.Only $355.00 at Gemvara
no photoMen's Round Peridot Sterling Silver Ring with Fire Opal - Octagon Ring
$355.00
Gemvara
Princess Black Onyx Sterling Silver Ring with Black Onyx & Fire Opal - Ianna Ring
A 5mm, princess-cut center stone is enhanced by accent gems set into this gorgeous band, handcrafted in your choice of gems and metals.Only $350.00 at Gemvara
no photoPrincess Black Onyx Sterling Silver Ring with Black Onyx & Fire Opal - Ianna Ring
$350.00
Gemvara
Round Emerald Sterling Silver Ring with Fire Opal & London Blue Topaz - Venus Band
Scalloped shells form a fluted pattern on each side of this feminine tapered band, carefully handcrafted in your choice of gems and metals.Only $220.00 at Gemvara
no photoRound Emerald Sterling Silver Ring with Fire Opal & London Blue Topaz - Venus Band
$220.00
Gemvara
Round Aquamarine Sterling Silver Ring with Green Tourmaline & Fire Opal - Liana Ring with Three Gems
This lovely leafy vine ring twines across the finger while brilliant gems bloom among the leaves.Only $190.00 at Gemvara
no photoRound Aquamarine Sterling Silver Ring with Green Tourmaline & Fire Opal - Liana Ring with Three Gems
$190.00
Gemvara
Sterling Silver Bracelet with Black Onyx & Fire Opal - Saturn Bangle
A true statement piece, this bangle's 17 round gemstones dazzle in a basket setting, carefully handcrafted in your choice of gems and metals.Only $595.00 at Gemvara
no photoSterling Silver Bracelet with Black Onyx & Fire Opal - Saturn Bangle
$595.00
Gemvara
Round Ruby Sterling Silver Ring with Fire Opal & Diamond - Venus Band
Scalloped shells form a fluted pattern on each side of this feminine tapered band, carefully handcrafted in your choice of gems and metals.Only $225.00 at Gemvara
no photoRound Ruby Sterling Silver Ring with Fire Opal & Diamond - Venus Band
$225.00
Gemvara
Sterling Silver Ring with Fire Opal & Citrine - Double Knots Ring
This gorgeous, contemporary setting forms a pair of knots, each enclosing a stunning, 3mm, prong-set stone. It's carefully handcrafted in your choice of gems and metals.Only $180.00 at Gemvara
no photoSterling Silver Ring with Fire Opal & Citrine - Double Knots Ring
$180.00
Gemvara
Round Fire Opal Sterling Silver Ring with Ruby & Citrine - Venus Band
Scalloped shells form a fluted pattern on each side of this feminine tapered band, carefully handcrafted in your choice of gems and metals.Only $210.00 at Gemvara
no photoRound Fire Opal Sterling Silver Ring with Ruby & Citrine - Venus Band
$210.00
Gemvara
Round Fire Opal Sterling Silver Ring with Emerald & Red Garnet - Venus Band
Scalloped shells form a fluted pattern on each side of this feminine tapered band, carefully handcrafted in your choice of gems and metals.Only $215.00 at Gemvara
no photoRound Fire Opal Sterling Silver Ring with Emerald & Red Garnet - Venus Band
$215.00
Gemvara
Round Fire Opal Sterling Silver Ring with Smoky Quartz & Black Diamond - Venus Band
Scalloped shells form a fluted pattern on each side of this feminine tapered band, carefully handcrafted in your choice of gems and metals.Only $210.00 at Gemvara
no photoRound Fire Opal Sterling Silver Ring with Smoky Quartz & Black Diamond - Venus Band
$210.00
Gemvara
Round Fire Opal Sterling Silver Ring with London Blue Topaz - Venus Band
Scalloped shells form a fluted pattern on each side of this feminine tapered band, carefully handcrafted in your choice of gems and metals.Only $205.00 at Gemvara
no photoRound Fire Opal Sterling Silver Ring with London Blue Topaz - Venus Band
$205.00
Gemvara
Round Peridot Sterling Silver Ring with Fire Opal & Tanzanite - Venus Band
Scalloped shells form a fluted pattern on each side of this feminine tapered band, carefully handcrafted in your choice of gems and metals.Only $205.00 at Gemvara
no photoRound Peridot Sterling Silver Ring with Fire Opal & Tanzanite - Venus Band
$205.00
Gemvara
Synthetic Opal, .50ct t.w. CZ Pendant Necklace in Silver. 18"
Cast an opulent glow with this heavenly pendant necklace. The synthetic opal with a great play of color is embraced by a frame of dazzling white CZs, .50 ct. t.w. Cable chain, springring clasp. Sterling silver pendant necklace. CZ weights are diamond...Only $70.00 at Ross-Simons
no photoSynthetic Opal, .50ct t.w. CZ Pendant Necklace in Silver. 18"
$70.00
Ross-Simons
Sterling Silver Bracelet with Fire Opal & Rock Crystal - Mercury Bangle
This hinged bangle bracelet has 19 vibrant round gemstones set in a circular granulated setting. Carefully handcrafted in your choice of gems and metals.Only $605.00 at Gemvara
no photoSterling Silver Bracelet with Fire Opal & Rock Crystal - Mercury Bangle
$605.00
Gemvara

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