Where is Scoria with secondary alteration found?
Scoria (volcanic rock) with secondary alteration/mineralization (e.g., chlorite, epidote, or lichen)
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Open the appScoria with secondary alteration 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 Scoria with secondary alteration
Volcanic regions worldwide
Anywhere scoria is found, subsequent alteration can occur. Notable locations include the Cascade Range (USA), Hawaiian Islands (USA), Canary Islands (Spain), Iceland, Italy (e.g., Vesuvius, Etna), Japan, and numerous other active and extinct volcanic provinces.
Hydrothermal alteration zones
Areas with active or past hydrothermal systems, where hot, mineral-rich fluids have circulated through volcanic rocks, are prime locations for secondary mineralization.
Weathered volcanic deposits
Older scoria deposits exposed to weathering and groundwater infiltration over long periods can develop significant secondary mineralization.
Collecting tips
- Look for color variations. Beyond the typical dark scoria color, look for patches or infillings of green, white, yellow, or other colors within the vesicles or on the surface, indicating secondary minerals or lichens.
- Examine vesicle infillings. Carefully inspect the interior of vesicles. Instead of empty voids, look for crystalline growths, powdery coatings, or solid fillings.
- Check for surface growths. Lichens often appear as crusty, leafy, or powdery patches on the rock surface, varying in color from white, gray, green, yellow, to orange.
- Consider the geological context. In volcanic areas, especially those with evidence of past hydrothermal activity or significant weathering, the likelihood of finding altered scoria increases.
Quick Check
- Color:
- Dark matrix with varied colors from secondary minerals (green, white, yellow, etc.) or lichens.
- Luster:
- Dull to earthy for scoria, varied for secondary minerals (vitreous, silky, earthy).
- Streak:
- Typically gray to brownish-black for scoria. Secondary minerals will have their characteristic streak (e.g., white for calcite, colorless for quartz).
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