Granite Identification Guide
A hands-on guide to identifying granite by its interlocking quartz, feldspar, and mica grains, with tests to separate it from gneiss and diorite.
Read the full Granite encyclopedia entry →
What Granite Looks Like
Granite is a coarse-grained, light-colored intrusive igneous rock. Because it cooled slowly underground, individual mineral grains are large enough to see with the naked eye and interlock tightly with no preferred orientation. Expect a speckled "salt and pepper" appearance dominated by pale minerals: glassy grey quartz, blocky pink, white, or cream feldspar, and scattered dark flakes of biotite mica or needles of hornblende. Overall color is usually pink, grey, or near-white depending on the feldspar.
Step-by-Step Field-ID Checklist
- Confirm coarse grain size. You should see distinct, interlocking crystals a few millimeters across or larger.
- Identify the minerals. Look for glassy quartz (no cleavage, conchoidal), shiny blocky feldspar (flat cleavage faces that catch light), and dark mica/amphibole.
- Check the texture. Grains are randomly oriented — no banding or layering. Banding suggests gneiss.
- Estimate composition. Granite is feldspar- and quartz-rich (over ~20% quartz), so it is mostly light.
- Test hardness. It scratches glass overall because quartz and feldspar are hard (6.5–7).
Key Diagnostic Tests
- Hardness: Quartz grains 7, feldspar 6 — granite as a whole scratches glass.
- Acid test: No reaction to dilute HCl (no carbonate), separating it from marble and limestone.
- Texture: Phaneritic (visibly crystalline) and equigranular to porphyritic with no foliation.
- Feldspar cleavage: Look for flat, reflective cleavage planes on feldspar grains; quartz shows no cleavage.
- Density: ~2.6–2.7, typical for a felsic rock.
Common Look-Alikes and How to Tell Them Apart
- Gneiss: Has the same minerals but shows distinct light/dark banding (foliation). Granite is unbanded and randomly oriented.
- Diorite: Darker, with little or no quartz and more plagioclase plus hornblende; diorite looks more black-and-white than pink/grey.
- Gabbro: Much darker and quartz-poor (mafic). Granite is pale and quartz-rich.
- Granodiorite: A close cousin with more plagioclase than alkali feldspar; granodiorite is greyer with fewer pink tones.
- Sandstone (when weathered): Sandstone is made of cemented rounded grains, feels gritty, and lacks interlocking crystals.
Where Granite Is Found
Granite forms the cores of mountain belts and continental crust, exposed as large batholiths, plutons, and domes. Classic exposures include the Sierra Nevada and New Hampshire (USA), Cornwall (UK), and shield regions worldwide. Look for it in eroded mountain cores, quarries, glacial erratics, and as durable boulders in streambeds.
Frequently asked questions
How can you tell if a rock is granite?
Granite is coarse-grained with visible, randomly oriented interlocking crystals of glassy quartz, blocky feldspar, and dark mica or hornblende. It scratches glass and does not fizz in acid.
What does granite look like?
A speckled, light-colored rock — pink, grey, or white — with a salt-and-pepper mix of pale feldspar and quartz dotted with dark mineral flakes.
Granite vs gneiss: what's the difference?
They share the same minerals, but gneiss shows alternating light and dark bands (foliation), while granite has randomly oriented grains and no banding.
Granite vs diorite: how do I tell them apart?
Granite is light-colored and quartz-rich, often with pink feldspar; diorite is darker, has little quartz, and looks more black-and-white from plagioclase and hornblende.
Where is granite found?
In the cores of mountain ranges and continental crust — as batholiths, plutons, quarries, and boulders worldwide, including the Sierra Nevada and New England in the USA.
Granite identified by the community
Recent Granite specimens identified with Rock Identifier.
