Where is Quartz in Basalt found?
SiO2 in Basalt
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Open the appQuartz in Basalt occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Quartz in Basalt
Deccan Traps, India
Extensive flood basalts known for abundant amygdaloidal fillings, including quartz, chalcedony, and zeolites.
Columbia River Basalt Group, USA
Vast flood basalts in the Pacific Northwest, often containing geodes and amygdules filled with quartz, agate, and other secondary minerals.
Paraná-Etendeka Province, South America/Africa
Large igneous province with basalts containing various secondary mineral infillings.
Iceland
Active volcanic island with numerous basaltic lava flows, where secondary mineralization in vesicles is common.
Brazil (especially Rio Grande do Sul)
Famous for large amethyst and agate geodes found within basaltic rocks.
Collecting tips
- Look for Vesicular Basalt. Focus on basaltic lava flows that show evidence of gas bubbles (vesicles). These are the primary sites for secondary mineral deposition.
- Examine Weathered Outcrops. Weathering can sometimes expose the more resistant quartz infillings, making them stand out from the softer basalt matrix.
- Check for Geodes and Amygdules. Look for rounded or irregular cavities filled with crystalline material. Geodes are typically hollow, while amygdules are completely filled.
- Utilize a Rock Hammer. Carefully break open basaltic rocks, especially those with visible vesicles, to reveal potential quartz infillings.
- Research Localities. Consult geological maps and local rockhounding guides for known occurrences of amygdaloidal basalts or agate/geode localities.
Quick Check
- Color:
- Dark gray to black (basalt) with colorless, white, or colored inclusions (quartz)
- Luster:
- Dull to sub-vitreous (basalt) with vitreous to waxy (quartz) inclusions
- Streak:
- White (quartz) on a streak plate; basalt typically has a dark gray to black streak, but the quartz inclusion itself will be white.
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