mineraloid
Common Opal (Green Opal / Pistachio Opal)
Hydrated silica (SiO2·nH2O)
Hardness: 5.5–6 (Mohs scale); Color: Pale light green to yellowish-green; Luster: Vitreous to waxy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 1.9–2.3
- Hardness
- 5
- Color
- Pale light green to yellowish-green
- Luster
- Vitreous to waxy
Identified More mineraloid →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5.5–6 (Mohs scale); Color: Pale light green to yellowish-green; Luster: Vitreous to waxy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 1.9–2.3
Formation & geological history
Formed from silica-rich groundwater filling cavities and fissures in volcanic or sedimentary rocks. Unlike precious opal, common opal lacks the internal structure to diffract light and show play-of-color. Typically associated with Tertiary and Quaternary geological deposits.
Uses & applications
Primary use is in lapidary work for cabochons, beads, and carvings. Also popular as a healing stone in metaphysical communities and as affordable specimens for beginner mineral collectors.
Geological facts
Common opal is technically a mineraloid rather than a mineral because it lacks a crystal structure. Green varieties often get their hue from inclusions of nickel or iron silicates, and they are sometimes misidentified as jade or chrysoprase.
Field identification & locations
Identify in the field by its waxy luster, lack of crystal faces, and smooth, curved (conchoidal) fracture surfaces that look like broken glass. Commonly found in Madagascar, Tanzania, Brazil, and the Western United States. For collectors, look for uniform color and translucency.
More like this
Other mineraloid specimens
Amber
Succinite (Organic Mineraloid)
mineral
Fulgurite
Fulgurite (Lechatelierite)
metamorphic
Black Obsidian
Volcanic Glass (SiO2 + impurities)
Igneous
Obsidian
Volcanic glass
igneous
Limonite (Ironstone)
Limonite (mixture of hydrated iron oxides, primarily Goethite α-FeO(OH))
mineral
Obsidian
Volcanic glass (SiO2 - Silicon Dioxide with impurities)
igneous