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Boulder Opal

OPAL

Jelly Opal
Yowah Nut Opal Hyalite Precious Opal Opalite

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 Black Onyx Sterling Silver Vintage-Inspired Ring with Fire Opal & Ruby - 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 Black Onyx Sterling Silver Vintage-Inspired Ring with Fire Opal & Ruby - Venus Band
$205.00
Gemvara
Sapphire, Ruby, Opal Ring 7 Carats (ctw) in Sterling Silver, Size 5
Sapphire, Ruby, Opal Ring 7 Carats (ctw) in Sterling Silver, Size 5 #68CD6264MG:V5. A striking combination of ruby, sapphire and opal form a beautiful 7.0 carat ring. These colored gemstones are crafted with sterling silver and matching earrings and...Only $99.00 at MyJewelryBox.com
no photoSapphire, Ruby, Opal Ring 7 Carats (ctw) in Sterling Silver, Size 5
$99.00
MyJewelryBox.com
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 Fire Opal Sterling Silver Ring with Fire Opal & White Sapphire - Dahlia Ring
Two rings of petals surround the center of this graceful star-shaped flower ring from Gemvara Essentials. Customize each ring of gems separately for endless design possibilities.Only $355.00 at Gemvara
no photoRound Fire Opal Sterling Silver Ring with Fire Opal & White Sapphire - Dahlia Ring
$355.00
Gemvara
Genuine Opal & Diamond-Accent Bracelet In Sterling Silver, White, Womens
Alluring and delicate, this genuine opal and diamond-accent pendant is crafted in brightly polished sterling silver. Metal: Sterling silverStone: Genuine opalOther Stones: Diamond accents Setting: ProngClosure: Lobster claspLength: 7 1/4in Gemstones...Only $124.98 at jcpenney
no photoGenuine Opal & Diamond-Accent Bracelet In Sterling Silver, White, Womens
$124.98
jcpenney
Round Fire Opal Sterling Silver Vintage-Inspired Ring with Sapphire & Alexandrite - 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 $230.00 at Gemvara
no photoRound Fire Opal Sterling Silver Vintage-Inspired Ring with Sapphire & Alexandrite - Venus Band
$230.00
Gemvara
Sterling Silver Promise Ring with Fire Opal & London Blue Topaz - Infinite Love Ring
Two people, two gems, linked for eternity in this classic ring that symbolizes infinite love. Infinity symbols surround the finger in an endless circle. Customize this design with your two birthstones or use personal symbolism to represent your union.Only $260.00 at Gemvara
no photoSterling Silver Promise Ring with Fire Opal & London Blue Topaz - Infinite Love Ring
$260.00
Gemvara
Oval Fire Opal Sterling Silver Engagement Ring - Ella Ring
Simply gorgeous. One oval cut gem in a streamlined bezel setting.Only $245.00 at Gemvara
no photoOval Fire Opal Sterling Silver Engagement Ring - Ella Ring
$245.00
Gemvara
Sterling Silver Mother's Ring with Red Garnet & Fire Opal - Double Embrace Ring
Two, 4mm round-cut gemstones are held in the curve of this stunning, contemporary design. Choose your gems and metal.Only $240.00 at Gemvara
no photoSterling Silver Mother's Ring with Red Garnet & Fire Opal - Double Embrace Ring
$240.00
Gemvara
Oval Fire Opal Sterling Silver Engagement Ring - Yara Ring
A single, stunning 8mm oval-cut stone is embraced by four prongs and a contemporary knot design. A brilliant display of your favorite gem and metal.Only $335.00 at Gemvara
no photoOval Fire Opal Sterling Silver Engagement Ring - Yara Ring
$335.00
Gemvara
Round Fire Opal Sterling Silver Mother's Ring with Sapphire - Liana Ring with Three Gems
This lovely leafy vine ring twines across the finger while brilliant gems bloom among the leaves.Only $215.00 at Gemvara
no photoRound Fire Opal Sterling Silver Mother's Ring with Sapphire - Liana Ring with Three Gems
$215.00
Gemvara
Round Fire Opal Sterling Silver Mother's Ring with London Blue Topaz - Quintessence Ring
Five sparkling gems cover the finger with brilliance in this classic style that is a Gemvara Essential.Only $260.00 at Gemvara
no photoRound Fire Opal Sterling Silver Mother's Ring with London Blue Topaz - Quintessence Ring
$260.00
Gemvara
Round Citrine Sterling Silver Vintage-Inspired Ring with Fire Opal & Smoky Quartz - 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 Citrine Sterling Silver Vintage-Inspired Ring with Fire Opal & Smoky Quartz - Venus Band
$205.00
Gemvara
Round Peridot Sterling Silver Vintage-Inspired 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 Vintage-Inspired Ring with Fire Opal & Tanzanite - Venus Band
$205.00
Gemvara
Round Fire Opal Sterling Silver Promise Ring with Black Onyx - Faye Ring
A gorgeous, 5mm round center stone is flanked by accent gems set into the band. Tastefully stunning.Only $345.00 at Gemvara
no photoRound Fire Opal Sterling Silver Promise Ring with Black Onyx - Faye Ring
$345.00
Gemvara

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