igneous
Vesicular Basalt with Opal or Quartz
Vesicular Basalt (Amorphous SiO2.nH2O if Opal)
Hardness: 5.5-7 (Mohs scale), Color: tan to grayish exterior with small translucent inclusions, Luster: earthy matrix with vitreous/pearly inclusions, Crystal Structure: amorphous or microcrystalline, Cleavage: none, Specific Gravity: 2.1-3.0
- Hardness
- 5
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Physical properties
Hardness: 5.5-7 (Mohs scale), Color: tan to grayish exterior with small translucent inclusions, Luster: earthy matrix with vitreous/pearly inclusions, Crystal Structure: amorphous or microcrystalline, Cleavage: none, Specific Gravity: 2.1-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava. The holes (vesicles) were formed by gas bubbles. Later, silica-rich fluids filled these voids, creating the clear, slightly iridescent inclusions seen in the specimen.
Uses & applications
Primarily used for geological study, decorative gardening, and occasionally low-grade gemstone recovery if the inclusions are precious opal.
Geological facts
The rainbow flash visible in the clear section suggests a small 'play of color,' which is the defining characteristic of opal. This specific combination is often found in volcanic regions of Ethiopia or Australia.
Field identification & locations
Identify by looking for a porous, rocky matrix containing glassy or jelly-like 'pockets.' Commonly found in ancient volcanic fields. Collectors should look for flashes of color within the clear amygdules.
