Identification guide · Igneous Rocks
How to Identify Granodiorite
Granodiorite has a coarse-grained, phaneritic texture showing visible interlocking crystals of gray to white plagioclase, less abundant pink or white orthoclase, glassy quartz, and dark biotite or hornblende, giving an overall salt-and-pepper gray appearance. Testing the hardness of individual grains rather than the whole rock is necessary, since quartz scratches glass easily while feldspar and mica are softer. There is no single cleavage or streak for the rock as a whole, since these properties belong to its component minerals. It is commonly confused with true granite, which contains proportionally more quartz and orthoclase feldspar relative to plagioclase.
Granodiorite identification checklist
| Color | Light gray, Gray, Pinkish gray, White with dark specks | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous to dull (mixed mineral grains) | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 6–7 | It scratches glass and a steel knife and cannot be scratched by a steel file. |
| Fracture | Uneven, granular | |
| Specific gravity | 2.65–2.73 | Ordinary rock-like heft (specific gravity about 2.69), similar to quartz. |
Granodiorite look-alikes and how to tell them apart
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Granodiorite vs Syenite →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Granodiorite vs Granite →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Granodiorite vs Monzonite →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Granodiorite identification FAQ
How can you tell if a rock is Granodiorite?
Check the color (light gray, gray, pinkish gray, and white with dark specks), the vitreous to dull (mixed mineral grains) luster, a Mohs hardness of 6–7. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Granodiorite?
Granodiorite has a Mohs hardness of 6–7. It scratches glass and a steel knife and cannot be scratched by a steel file.
What is the difference between Granodiorite and Syenite?
Granodiorite (Mohs 6–7, vitreous to dull (mixed mineral grains) luster) and Syenite (Mohs 5.5–6.5, vitreous (feldspar crystals) luster) look alike, but hardness, streak and heft usually separate them. See the full Granodiorite vs Syenite comparison for a side-by-side table.
Is Granodiorite worth anything?
Entry-level Granodiorite specimens sell for around $1, typical collector pieces about $10, and premium examples $75 or more depending on size, quality and locality.
What color is Granodiorite?
Granodiorite is most often light gray, gray, pinkish gray, and white with dark specks. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
