Guide
Opal specimens for sale
43 for sale · $115–$265,000 USD
349 in the gallery
Opal is a mineraloid consisting of hydrated silica (SiO2·nH2O) that lacks a crystalline structure, giving it a smooth, glassy appearance and a soft, waxy luster. It is most renowned for its play-of-color, a diffraction phenomenon that reveals brilliant flashes of color as light interacts with its submicroscopic silica spheres. In many specimens the color range shifts with viewing angle, producing a shimmering, opalescent look prized by collectors. Opal occurs in a variety of forms, from solid, glassy-bodied pieces to porous opal and common opal with a more opaque, milky appearance.
- Formula
- SiO2 · nH2O
- Rarity
- Common
- Stability
- Moderately Stable
- Collector interest
- High Interest
- Classification notes
- Silicate minerals; hydrated amorphous silica (opal group)
Key characteristics
- Crystal system
- amorphous
- Mohs hardness
- 5.5–6.5
- Specific gravity
- 1.9–2.3
- Luster
- vitreous, resinous, waxy, greasy, dull
- Transparency
- transparent, translucent, opaque
- Color
- colorless, white, gray, black, brown, red, orange, yellow, green, blue, violet, pink
- Streak
- white
- Cleavage
- none
- Fracture
- conchoidal, subconchoidal, uneven
- Crystal habit
- botryoidal, reniform, stalactitic, druzy, granular, massive
- Gem mineral
- Fluorescent: white, green
- Classic / historic
Buy Opal specimens
View all 43Where Opal is found
Top localities
- Tsehay Mewcha33 specimens
- San Luis Potosí19 specimens
- South Wollo Zone18 specimens
- Zacatecas14 specimens
- Opal Butte13 specimens
- Erongo Mountains6 specimens
- Lightning Ridge5 specimens
- Queensland5 specimens
- Centre-Val de Loire4 specimens
- South Australia3 specimens
Guides
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About Opal
Significant specimen sources include Australia, Hungary, Mexico, Ethiopia, and the United States, where opal forms in a range of geological settings from sedimentary nodules to volcanic silica-rich veins. Australian opals, especially from fields like Coober Pedy and Lightning Ridge, are celebrated for intense play-of-color and larger, well-formed buds; Mexican and Hungarian opals are often prized for their distinctive body tones and patterning. Collectors value opal for its aesthetic versatility and the excitement of color shifts, as well as its historical significance in mineral and gem collections.
