📜 Key facts
| Age | Usually Miocene (about 20–5 million years old) |
|---|---|
| Origin & sources | Nevada and Idaho (USA), Indonesia and Slovakia. |
| Composition | Wood replaced by opal, often keeping its grain. It is sometimes precious, as in Virgin Valley, Nevada. Opal is hydrated amorphous silica (SiO₂·nH₂O), Mohs 5.5–6.5. |
How it forms
Silica-rich water seeped into cracks, cavities and fossils, then slowly evaporated. Tiny silica spheres settled out. In precious opal they are stacked in a neat, regular grid that diffracts light into play-of-colour. In common opal they are jumbled.
Mineral data: see Opal.
🌍 Where it's found
- Type locality
- Notable source / deposit
- Country of origin
Marker positions are approximate (region or locality level). Type localities from Wikidata; notable sources curated by Crystopedia.
✨ Opal family

Black OpalMineral variety

Blue OpalMineral variety

Boulder OpalMineral variety

Chocolate OpalMineral variety

Common OpalMineral variety
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Crystal OpalMineral variety
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Dendritic OpalMineral variety
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Ethiopian OpalMineral variety

Fire opalMineral variety
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Green OpalMineral variety

Honey OpalMineral variety

HyaliteMineraloid variety

Matrix OpalMineral variety

OpalIMA mineral species

Opal Doublet & TripletMineral variety

OpaliteNatural glass

Opalized FossilFossil

Pink OpalMineral variety
◆
Precious opalGem material

Synthetic OpalMineral variety
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Virgin Valley OpalMineral variety

White OpalMineral variety
Learn more
Mineral variety
OrangeMulticolor & Iridescent
Root
Healing crystal

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