No two opals are alike. Each stone holds a private universe of shifting colour — flashes of green, blue, fire and violet that move across the surface as you tilt it. The opal is October's birthstone and one of the most personal gems in fine jewellery.
What an opal actually isUnlike most gems, an opal isn't a true crystal. It is hydrated silica — microscopic spheres of silicon dioxide stacked in regular three-dimensional grids, with up to 10% water trapped inside. When light enters, those silica spheres diffract it into spectral colour, producing the famous "play of colour" that no other gem can match. The phenomenon is purely physical, not chemical: the colours come from the architecture of the stone, not from impurities.
The main types of opal- White (light) opal: a milky pale body colour with rainbow flashes. The most common opal and the entry point for most collectors.
- Black opal: a dark body (grey to black) that makes the play of colour glow with extraordinary intensity. The most valuable type, mined almost entirely at Lightning Ridge, Australia.
- Boulder opal: opal embedded in a host rock (typically ironstone). The natural backing intensifies colour. A speciality of Queensland, Australia.
- Crystal opal: transparent or translucent with vivid flashes — looks like liquid trapped in glass.
- Fire opal: orange to red body colour, sometimes with little to no play of colour. Mined mainly in Mexico, often facetted rather than cabochon.
- Ethiopian (Welo) opal: a more recent discovery (2008) producing remarkable crystal-clear stones with bright fire at accessible prices.
Romans called opal opalus ("precious stone") and considered it the most valuable of all gems because it contained the colours of every other. Pliny the Elder wrote that opal held "the fire of the carbuncle, the brilliant purple of amethyst, and the sea-green of emerald, all shining together."
The stone was associated with hope, truth and creative inspiration. In some Eastern traditions opal was considered the stone of the eye and used as protective amulets. The Victorian-era superstition that opal brings bad luck appears to trace to a single 1829 Walter Scott novel and to merchant rivals trying to suppress its competition with diamond — fine-jewellery historians today reject the superstition entirely.
Modern symbolism connects the opal with:
- Creativity and inspiration — favoured by writers and artists.
- Emotional truth — an "honest" stone for moments of self-discovery.
- Hope — the original Roman association with new beginnings.
Standard 4 Cs don't apply. For opal, the dimensions of value are:
- Body tone: from N1 (jet black) through N9 (white). Darker bodies make colour more visible.
- Brightness: graded B1 (brilliant) to B5 (subdued). Higher brightness commands a premium.
- Pattern: "harlequin" (broad geometric flashes) is the rarest and most valuable; "pinfire" and "flagstone" are also prized.
- Dominant colour: red is the rarest play colour, followed by orange, yellow, green and finally blue.
- Cut and shape: opals are almost always shaped as cabochons or freeform to maximise the colour patches.
An opal contains water, so it deserves more thoughtful care than other gems:
- Avoid sudden temperature changes — they can cause "crazing" (fine cracks).
- Don't store in a hot, dry safe — keep in a soft pouch with a small humidity source if your home is very dry.
- Never use ultrasonic or steam cleaners.
- Remove before swimming or showering — chlorinated and very hot water are the main risks.
- Clean with a damp cloth, never with detergents or jewellery-cleaning fluid.
Mohs hardness is 5.5–6.5, so set opals in protective bezels for rings — never in claws if the wearer is hands-on.
How to wear opal- Pendants and earrings are the safest formats — minimal impact risk.
- Statement rings for occasion wear, set in protective bezels with a substantial gold rim.
- Stacking with diamonds creates striking contrast — the opal's quiet glow against diamond fire is a classic juxtaposition.
- Engagement rings have surged in popularity for couples wanting an alternative to diamond — make sure the wearer accepts the extra care required.
Is the bad-luck superstition real?
No. It traces to Walter Scott's 1829 novel Anne of Geierstein and was reinforced by 19th-century jewellery merchants protecting diamond sales. Queen Victoria openly disregarded the superstition and gave opals to her daughters as wedding gifts.
Doublet, triplet, solid — what's the difference?
A solid opal is a single piece of natural stone. A doublet bonds a thin opal slice to a dark backing. A triplet adds a clear quartz cap on top for protection. Doublets and triplets are far less expensive but should be disclosed and cared for differently — never submerge them in water for long periods.
Is Ethiopian opal worth buying?
Yes — high-quality Welo opal can rival Australian stones in beauty. Be aware that some Ethiopian opal is "hydrophane" (more porous) and may temporarily change colour when wet. Always buy from a jeweller who can identify and disclose this.
Browse our necklaces for opal pendant styles or read more on black gemstones if you're drawn to opal's deeper relatives.
