mineral

Precious Opal in Matrix

Hydrated Silica (SiO2·nH2O)

Hardness: 5.5-6.5 Mohs; Color: White to tan matrix with blue to violet play-of-color; Luster: Sub-vitreous to waxy; Structure: Amorphous silica spheres; Cleavage: None; SG: 1.9-2.3.

Hardness: 5
Color: White to tan matrix with blue to violet play-of-color
Luster: Sub-vitreous to waxy

Identified June 27, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5 Mohs; Color: White to tan matrix with blue to violet play-of-color; Luster: Sub-vitreous to waxy; Structure: Amorphous silica spheres; Cleavage: None; SG: 1.9-2.3.

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities in volcanic or sedimentary rocks. The silica precipitates as microscopic spheres which diffract light. Most deposits range from Cretaceous to Tertiary ages.

Uses & applications

Primarily used as a gemstone in jewelry (cabochons) and as a lapidary specimen for collectors.

Geological facts

The 'play-of-color' seen in this image is caused by the diffraction of light by regularly stacked silica spheres. Opal is Australia's national gemstone, and matrix opals like this are frequently found in Queensland.

Field identification & locations

Identify in the field by looking for flashes of spectral colors (fire) within a host rock matrix. Common in arid regions where ancient geothermal or ground water activity occurred. Look for vitreous seams in basalt or sandstone.