igneous
Weathered volcanic rock, likely andesite
Andesite (plagioclase–pyroxene volcanic rock), identification tentative
AI-generated identification · may be incorrectDark gray-green, fine-grained and massive, with rough weathered surfaces and possible small pale feldspar crystals. Typical andesite hardness is about 6–7 Mohs, with a dull to faintly vitreous luster, interlocking microscopic crystals, and no obvious cleavage; density is roughly 2.5–2.8 g/cm³.
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Physical properties
Dark gray-green, fine-grained and massive, with rough weathered surfaces and possible small pale feldspar crystals. Typical andesite hardness is about 6–7 Mohs, with a dull to faintly vitreous luster, interlocking microscopic crystals, and no obvious cleavage; density is roughly 2.5–2.8 g/cm³.
Formation & geological history
Forms when intermediate-composition magma cools at or near the surface, commonly in volcanic arcs. The specimen may be relatively young by geological standards; its exact age cannot be determined visually.
Uses & applications
Used locally as crushed aggregate, road material, riprap, and building stone. Unusual fresh pieces may have modest collector interest, but it is not normally a gemstone.
Geological facts
The greenish coloration may reflect chlorite or other secondary alteration minerals, common in volcanic rocks exposed to hydrothermal fluids or tropical weathering.
Field identification & locations
The appearance is consistent with volcanic rocks widespread around Luzon, Philippines, including andesite and altered basalt. Confirm with a fresh broken surface, a hand lens, streak (usually none), and ideally density or thin-section testing; distinguishing andesite from basalt requires mineral/compositional analysis.
