Peruvian Blue Opal Identification Guide
Identifying Peruvian blue opal by its soft turquoise body color and lack of fire, and telling it from larimar and chrysocolla.
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What Peruvian Blue Opal Looks Like
Peruvian blue opal is a common (non-precious) opal colored a soft sky-blue to blue-green or turquoise by trace copper. Unlike precious opal it shows no play-of-color (no spectral fire); instead it has an even, milky to translucent body and a waxy to vitreous luster. Stones are often mottled with white, gray, or brownish matrix patches and can range from near-transparent watery blue to opaque robin's-egg blue. It is cut into cabochons and beads and prized for its calming pastel tone.
Step-by-Step Field ID Checklist
- Judge the color. A pastel sky-blue to turquoise body, sometimes with green tints, is the signature.
- Confirm no play-of-color. Tilt it under light — Peruvian blue opal glows evenly with no flashing rainbow fire.
- Check translucency. Most pieces are translucent to semi-opaque with a slightly waxy surface.
- Look for matrix. White or brown host rock veining is common and helps confirm natural origin.
- Test hardness. It scratches with a steel knife at the edges (Mohs ~5.5–6.5), softer than quartz.
Key Diagnostic Tests
- Hardness: ~5.5–6.5; a steel blade or quartz will scratch it.
- Streak: White.
- Fracture: Conchoidal, brittle; no cleavage.
- Luster: Waxy to vitreous.
- Density: ~2.0–2.2, light — opal is hydrated silica with up to ~10% water.
- Acid/magnetism: No reaction; non-magnetic.
Common Look-Alikes and How to Tell Them Apart
- Larimar (blue pectolite): Shows a distinctive white-and-blue branching, fibrous pattern; harder to scratch than opal in places and has a different, streaky texture. Larimar is a pectolite, not silica.
- Chrysocolla / gem silica: Often a more intense electric blue-green; gem silica is chalcedony-hardness (7) and will not scratch, unlike softer opal.
- Turquoise: More opaque, often with a webbed matrix; turquoise is a phosphate and feels different, and it can react to solvents.
- Hemimorphite (blue): Botryoidal, glassier, and harder.
- Dyed howlite or magnesite: Uniform dye color often pooling in veins; opal's blue is more diffuse and natural-looking.
The combination of soft hardness, no play-of-color, and a diffuse pastel blue separates it from harder silica imitations.
Where Peruvian Blue Opal Is Found
As the name says, it comes chiefly from the Andes of Peru, notably the Acari mine in the Arequipa region, where copper mineralization tints the opal. It forms in volcanic and copper-rich hydrothermal settings. Most material reaching the market is mined and cut in Peru.
Frequently asked questions
How can you tell if Peruvian blue opal is real?
Real Peruvian blue opal is a soft diffuse sky-blue to turquoise with no rainbow play-of-color, a hardness around 5.5–6.5 that a knife can scratch, and often natural white or brown matrix.
Peruvian blue opal vs larimar — what's the difference?
Larimar is blue pectolite with a distinctive white branching, fibrous pattern, while Peruvian blue opal is hydrated silica with a smoother, more uniform pastel body and waxy luster.
Does Peruvian blue opal have fire?
No. It is a common opal, so it shows an even body color rather than the flashing spectral play-of-color seen in precious opals like Australian or Ethiopian opal.
What gives Peruvian blue opal its color?
Trace amounts of copper in the silica give it the characteristic soft blue to blue-green tint, reflecting its origin in copper-rich Andean volcanic deposits.
Is Peruvian blue opal the same as chrysocolla?
No, though they can look similar. Chrysocolla is a copper silicate often harder when intergrown with chalcedony (gem silica), whereas Peruvian blue opal is softer hydrated opal.