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Fireworks. Jellyfish. Galaxies. Lightning. Opal’s shifting play of kaleidoscopic colours is unlike any other gem.

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Most opals are cut as cabochons; this one from Ethiopia weighs 20.86 ct.

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Unique Beauty

The play-of-colour displays the entire spectrum over a light grey background.

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Bright flashes of colour skip across this stone’s surface.

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Hidden Beauty

Opal forms as irregular nodules or seams in volcanic or sedimentary rocks.

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Rare Phenomena

Play-of-colour results when light interacts with orderly stacks of spheres.

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This opal nodule displays the promise of intense play-of-colour.

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About Opal

"The Path of Enlightenment" Necklace

Because opal has the colours of other gems, the Romans thought it was the most precious and powerful of all. The Bedouins believed that opals contained lightning and fell from the sky during thunderstorms. When Australia’s mines began to produce opals commercially in the 1890s, it quickly became the world’s primary source for this October birthstone.

Opal Description

Opal History and Lore

Birthstones & Anniversaries

Opal is an October birthstone.

0.2 Microns

Grids of silica spheres 0.2 microns in size create red play-of-colour flashes.

20% Water

Opal contains up to 20% water trapped in its silica structure.


The novel “Anne of Geierstein” gave opal a reputation of being unlucky.


  • Mineral: Hydrated Silica
  • Chemistry: SiO2•nH2O
  • Color: All colours
  • Refractive index: 1.37-1.47
  • Birefringence: None
  • Specific gravity: 2.15 (+0.08, -0.90)
  • Mohs Hardness: 5 to 6.5


There are a number of processes used to alter the colour or apparent clarity, or to improve the durability of gems.

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Some gemstones have synthetic counterparts that have essentially the same chemical, physical and optical properties, but are grown by man in a laboratory.

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Any gem can be imitated – sometimes by man-made materials or by natural materials chosen by man to impersonate a particular gem.

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gem love

Why We Love This Gemstone


When opal formed, silica gel filled crevices in rock. As water evaporates, the silica is deposited in the form of tiny spheres.

Interaction with Light

Opal’s flashing play-of-colour is caused by diffraction of light by silica spheres stacked like tiny Ping-Pong balls in a box.


Opal’s arrays of silica spheres form a fantastic variety of patterns and colours. No two opals are exactly alike.

Quality Factors

Play-of-colour, intensity, and pattern are important value factors.


quality factors

Opal’s spectacular play-of-colour can display all the colours of the rainbow.


quality factors

Experts expect different levels of clarity for different types of opals.


quality factors

Fine opals are often cut into irregular shapes that keep as much play-of-colour as possible.

Carat Weight

quality factors

Opal has relatively low density so even larger sizes can be comfortable to wear.

Opal Quality Factors: The Comprehensive Guide


Explore sources, gemmological research and the role of gems in history.

Queensland Opal Fields: Home of the Unique Australian Boulder Opal

Tao Hsu, Andrew Lucas and Vincent Pardieu , Jan 24, 2017 Read Article
Color bars on top and sides of 3,019 ct rough opal

The Challenges of Cutting a Large Gem Opal Rough

Theodore Grussing , Aug 3, 2016 Read more in English
Underground opal mining in Koroit

Splendour in the Outback: A Visit to Australia’s Opal Fields

Tao Hsu, Andrew Lucas, and Vincent Pardieu , Feb 1, 2016 Read more in English

New Deposit of Black Opal from Ethiopia

Lore Kiefert, Pierre Hardy, Tewodros Sintayehu, Begosew Abate, and Girma Woldetinsae , Jan 30, 2015 Read more in English