How to Identify Granite: What to Look For and Home Tests

Granite-type rocks cooled slowly underground, so their crystals grew large enough to see without a lens. Look for interlocking grains of two or three colors with no layering and no holes. The properties that identify Granite — color: Light-colored felsic minerals (quartz, potassium feldspar, plagioclase) plus dark-colored mafic minerals (biotite, hornblende) give a 'salt and pepper' speckled appearance. For a rock, texture and grain size matter more than any single hardness number.

• Mineral-composition test: granite's felsic minerals are quartz, potassium feldspar, and plagioclase feldspar; its mafic minerals are biotite and hornblende.

• Gneiss: Granite's crystals are interlocking but not aligned (no foliation); gneiss is a metamorphic rock whose minerals are aligned into visible banded foliation.
• Gabbro: Granite is light-colored because it is richer in silica; gabbro has lower silica content and is dark-colored.

Yosemite National Park (part of the granite batholith of California's Sierra Nevada).

Photograph a fresh, unweathered surface in daylight, then a second shot of any crystal faces or broken edge. Include a coin for scale. If you did a streak test, photograph the streak next to the specimen. The app suggests the likely mineral or rock; confirm with hardness and the tests above before you label it.

Granite is a rock (an aggregate of multiple minerals), so it has no single Mohs hardness or specific gravity value — both fields are left blank. The Illinois State Geological Survey guide also confirms granite is 'one of the most widespread intrusive ... igneous rocks' (same Gutenberg source as above).