Opal
Common Opal
Common opal (sometimes called 'potch' in the trade) makes up the overwhelming majority of all opal actually mined worldwide, even though it's the version almost nobody names specifically — most opal, whatever the color, simply lacks the ordered internal structure needed to produce play of color, and that unglamorous majority is what 'common opal' honestly refers to.
The geology — what Common Opal actually is
- Mineral class
- Mineraloid (hydrated amorphous silica, opal without play of color)
- Chemical formula
- SiO2·nH2O
- Crystal system
- Amorphous (no crystal structure)
- Mohs hardness
- 5.5–6.5
What causes the color: Color varies widely by locality and trace-element content — white, grey, yellow, brown, blue, pink, and more all occur; what defines this category isn't a specific color at all, but the absence of the regularly stacked microscopic silica-sphere structure that produces precious opal's rainbow flash.
How it forms: Forms through the same basic process as precious opal — silica-rich groundwater depositing hydrated silica in rock cavities — but without the uniform sphere sizing and packing regularity needed for light diffraction; most opal deposits worldwide produce overwhelmingly common, not precious, material.
- Found in opal-producing regions worldwide, including Australia, Mexico, Peru, and the United States, typically as the bulk byproduct alongside any precious opal a deposit also yields
Treatments & imitations: Sometimes dyed to imitate more valuable colored opal varieties, which should be disclosed; because common opal itself has modest commercial value, deliberate high-effort fakery is less common than simple honest sale as an affordable decorative material.
Real vs. fake: Common opal shares opal's characteristic softness (Mohs 5.5–6.5) and slightly waxy-to-vitreous luster; the simplest test distinguishing it from precious opal is straightforward observation — no shifting rainbow flash under angled light means it's common, not precious.
Potch: the same mineraloid without the diffraction
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- Common opal carved piece
Without the ordered silica-sphere structure that produces play of colour, this is opal with lustre and body colour only, and priced accordingly. It is sometimes dyed to imitate the precious varieties, which should be disclosed.
The tradition — how people use Common Opal
Historical use: As the majority form of opal mined throughout history, common opal has been used ornamentally and in beadwork across many cultures for a very long time, even when the more famous precious opal variety gets most of the historical attention in gem literature.
Metaphysical tradition: Modern crystal-healing tradition frames common opal simply, drawing on opal's broad reputation for emotional and creative themes without the added play-of-color mystique attached to precious opal specifically.
How to use it: Cut as cabochons, beads, and carved decorative objects; an affordable, widely available way to enjoy opal's characteristic soft luster without precious opal's higher price point.
Cleansing & care: Like all opal, common opal needs gentle handling — avoid extreme dryness and heat, skip harsh chemicals and ultrasonic cleaning, and use mild soap and water only when needed.
Frequently asked questions
What's the actual difference between common opal and precious opal?
Both are the same basic material (hydrated amorphous silica), but precious opal has a regular, uniform internal structure of stacked microscopic silica spheres that diffracts light into a rainbow play of color. Common opal lacks that regularity, so it shows solid color without the flash — and it makes up the large majority of all opal actually mined.
Related crystals
Opal
Silica Mineraloid
Like obsidian, opal is technically a mineraloid rather than a true crystalline mineral — but unlike obsidian's amorphous glass, opal's structure is a regular, ordered arrangement of microscopic silica spheres, and it's that structure, not any pigment, that produces precious opal's famous rainbow play-of-color. Opal also uniquely carries water within its own structure (roughly 3-21% by weight), which makes it one of the more fragile, care-sensitive gems in common use — a genuine physical vulnerability, not folklore, tied directly to a real 19th-century superstition that dented its reputation for decades.
Pink Opal
Opal
Pink opal is another common-opal variety — soft pink, generally without play of color — that's sourced primarily from the Andes, sharing its general geological story with Peruvian blue opal but colored by a completely different trace element entirely.
Peruvian Blue Opal
Opal
Peruvian blue opal is a genuinely uncommon opal variety on two counts: blue is a rare bodycolor for opal generally, and this specific translucent blue-green material, sourced from the Andes, typically shows no play of color at all, distinguishing it clearly from the rainbow-flashing precious opal most people picture.
Sources and factual basis for the geology above: see our methodology.