igneous
Altered volcanic rock, possibly andesite
Likely porphyritic andesite or dacite with secondary chlorite/epidote and quartz–calcite veins
AI-generated identification · may be incorrectGray-green, fine-grained and weakly porphyritic, with pale patches and rusty weathering. Likely hardness about 5–7 overall; dull to slightly waxy luster, no obvious cleavage, and massive texture. Exact mineralogy cannot be confirmed from a photograph.
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Physical properties
Gray-green, fine-grained and weakly porphyritic, with pale patches and rusty weathering. Likely hardness about 5–7 overall; dull to slightly waxy luster, no obvious cleavage, and massive texture. Exact mineralogy cannot be confirmed from a photograph.
Formation & geological history
Probably volcanic lava altered by hydrothermal fluids, producing green chlorite/epidote and pale quartz or calcite. Such rocks are commonly Cenozoic to Mesozoic in volcanic belts; the area near 24.8°N, 107.4°W in Sinaloa plausibly contains altered volcanic rocks.
Uses & applications
Ordinary andesite is used locally as aggregate, road stone, riprap, and building stone. This hand specimen has mainly educational or modest collector value.
Geological facts
The green color often reflects propylitic alteration rather than a single green mineral. Pale areas may be feldspar phenocrysts, quartz, calcite, or weathered alteration zones.
Field identification & locations
Identify in the field by its hard, compact volcanic texture, scattered light crystals, green-gray alteration, and lack of distinct sedimentary layering or strong foliation. A fresh streak, hand lens, acid test on pale material, and hardness test would help distinguish calcite-rich from quartz-rich patches.
