igneous
Coarse granite (likely weathered biotite granite)
Granite; quartz + feldspar + biotite/hornblende, approximate composition 20–60% quartz and abundant K-feldspar/plagioclase
AI-generated identification · may be incorrectLight gray, coarse-grained, speckled white/pink feldspar, glassy gray quartz, and dark mica/amphibole; interlocking crystalline texture. Mohs hardness about 6–7; vitreous quartz luster, no overall cleavage, specific gravity about 2.63–2.75. The surface appears strongly weathered and iron-stained.
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Physical properties
Light gray, coarse-grained, speckled white/pink feldspar, glassy gray quartz, and dark mica/amphibole; interlocking crystalline texture. Mohs hardness about 6–7; vitreous quartz luster, no overall cleavage, specific gravity about 2.63–2.75. The surface appears strongly weathered and iron-stained.
Formation & geological history
Slow cooling of silica-rich magma deep within the crust, producing large crystals; later uplift and tropical weathering exposed it. Exact age cannot be determined visually; granitic rocks around Luzon commonly range from Mesozoic to Cenozoic.
Uses & applications
Used as building stone, aggregate, monuments, countertops, and decorative slabs; attractive pieces may be collected, though this specimen appears ordinary and weathered.
Geological facts
The dark minerals are likely biotite or hornblende, while rusty orange areas are iron-oxide weathering products. Granite commonly develops rounded, crumbly surfaces through spheroidal weathering.
Field identification & locations
Likely plausible near 14.6°N, 121.0°E, where weathered volcanic and intrusive rocks occur in the broader Luzon region. Confirm by checking for visible quartz and feldspar grains, a scratch resistance near glass, and lack of consistent layering; acid testing is not diagnostic for granite.
