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 Fire Opal Sterling Silver Engagement Ring - Aeryn Round Ring
A 5mm, round-cut center stone is captured in a brilliant circle of your favorite precious metal.Only $285.00 at Gemvara
no photoRound Fire Opal Sterling Silver Engagement Ring - Aeryn Round Ring
$285.00
Gemvara
Oval Fire Opal Sterling Silver Engagement Ring with Pink Tourmaline & Peridot - Freya Ring
A 6mm, oval center stone is enhanced by accent gems set into this gorgeous band, handcrafted in your choice of gems and metals.Only $385.00 at Gemvara
no photoOval Fire Opal Sterling Silver Engagement Ring with Pink Tourmaline & Peridot - Freya Ring
$385.00
Gemvara
Sterling Silver Promise Ring with Aquamarine & Fire Opal - Two Hearts Ring
Two hearts meet in one simply perfect ring style. Create this style in your birthstones to add extra meaning.Only $225.00 at Gemvara
no photoSterling Silver Promise Ring with Aquamarine & Fire Opal - Two Hearts Ring
$225.00
Gemvara
Sterling Silver Promise Ring with Fire Opal - Infinity Twist Band
A strand of stones intertwines with a strand of metal to create this delicate ring. It is handcrafted in your choice of gems and metals.Only $385.00 at Gemvara
no photoSterling Silver Promise Ring with Fire Opal - Infinity Twist Band
$385.00
Gemvara
Round Green Tourmaline Sterling Silver Vintage-Inspired Ring with Citrine & 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 $205.00 at Gemvara
no photoRound Green Tourmaline Sterling Silver Vintage-Inspired Ring with Citrine & Fire Opal - Venus Band
$205.00
Gemvara
Sterling Silver CZ, Rainbow Fire Australian Black Opal Doublet (Boulder Opal) Pendant
Handmade by Master Artisan. See more details at JeGem.com.Only $116.99 at JeGem.com
no photoSterling Silver CZ, Rainbow Fire Australian Black Opal Doublet (Boulder Opal) Pendant
$116.99
JeGem.com
Blue Opal Doublet and Black Agate Ring in 14kt Yellow Gold
Be a little mysterious with this deep, dark, free-form ring. A blue opal doublet is boldly framed with 14kt yellow gold and black agate. 14kt yellow gold ring. Opal birthstones are the perfect gift for October birthdays.Only $295.00 at Ross-Simons
no photoBlue Opal Doublet and Black Agate Ring in 14kt Yellow Gold
$295.00
Ross-Simons
Sterling Silver Ring with Fire Opal & Iolite - Rhone Band
Seven 2.5mm, round-cut stones gleam and flow along the channel of this sleek, modern band, handcrafted in your choice of gemstones and metals.Only $265.00 at Gemvara
no photoSterling Silver Ring with Fire Opal & Iolite - Rhone Band
$265.00
Gemvara
Round Fire Opal Sterling Silver Mother's Ring with Yellow Sapphire - Triple Twist Ring
A Mobius strip of precious metal curves around three gemstones in a stylish ring style.Only $355.00 at Gemvara
no photoRound Fire Opal Sterling Silver Mother's Ring with Yellow Sapphire - Triple Twist Ring
$355.00
Gemvara
Sterling Silver Ring with Peridot & Fire Opal - Rhone Band
Seven 2.5mm, round-cut stones gleam and flow along the channel of this sleek, modern band, handcrafted in your choice of gemstones and metals.Only $255.00 at Gemvara
no photoSterling Silver Ring with Peridot & Fire Opal - Rhone Band
$255.00
Gemvara
Round Fire Opal Sterling Silver Vintage-Inspired Ring with Diamond & 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 $220.00 at Gemvara
no photoRound Fire Opal Sterling Silver Vintage-Inspired Ring with Diamond & Red Garnet - Venus Band
$220.00
Gemvara
Round White Sapphire Sterling Silver Vintage-Inspired Ring with Fire Opal & Pink Sapphire - 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 White Sapphire Sterling Silver Vintage-Inspired Ring with Fire Opal & Pink Sapphire - Venus Band
$210.00
Gemvara
Round Alexandrite Sterling Silver Mother's Ring with Fire Opal - Liana Ring with Three Gems
This lovely leafy vine ring twines across the finger while brilliant gems bloom among the leaves.Only $235.00 at Gemvara
no photoRound Alexandrite Sterling Silver Mother's Ring with Fire Opal - Liana Ring with Three Gems
$235.00
Gemvara
Round Fire Opal Sterling Silver Promise Ring - Petite Claddagh Ring
A petite version of the traditional Irish Claddagh Ring. This ring is given as a token of love or marriage and is carefully handcrafted in your choice of gems and metals.Only $135.00 at Gemvara
no photoRound Fire Opal Sterling Silver Promise Ring - Petite Claddagh Ring
$135.00
Gemvara
Round Fire Opal Sterling Silver Promise Ring - Two Paths Solitaire Ring
Two paths and two lives meet to hold a glittering gem representing one love in this elegant twist on a classic solitaire.Only $300.00 at Gemvara
no photoRound Fire Opal Sterling Silver Promise Ring - Two Paths Solitaire Ring
$300.00
Gemvara

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Available OPAL specimens:
see this List of ALL specimens including SOLD ones
 

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