Identification guide · Igneous Rocks
How to Identify Diorite
Diorite shows a coarse, fully crystalline, speckled texture, dominated by white to gray plagioclase feldspar and black hornblende or biotite in roughly balanced amounts. Overall hardness is around 6, reflecting its feldspar content, and there is no rock-scale cleavage, only mineral-scale cleavage in its component crystals. It is distinguished from granite by its scarcity of quartz and pink potassium feldspar, and from gabbro by its lighter overall color and more sodium-rich plagioclase.
Diorite identification checklist
| Color | Salt-and-pepper gray, Dark gray, Black and white speckled | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous to dull (granular) | 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 | 2.8–3.0 | Ordinary rock-like heft (specific gravity about 2.9), similar to quartz. |
Diorite 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. Diorite vs Gabbro →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Diorite vs Rhyolite →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Diorite vs Granite →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Diorite vs Larvikite →
Diorite identification FAQ
How can you tell if a rock is Diorite?
Check the color (salt-and-pepper gray, dark gray, and black and white speckled), the vitreous to dull (granular) luster, a Mohs hardness of 6–7. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Diorite?
Diorite 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 Diorite and Gabbro?
Diorite (Mohs 6–7, vitreous to dull (granular) luster) and Gabbro (Mohs 5–6.5, dull to vitreous (in crystals) luster) look alike, but hardness, streak and heft usually separate them. See the full Diorite vs Gabbro comparison for a side-by-side table.
Is Diorite worth anything?
Entry-level Diorite 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 Diorite?
Diorite is most often salt-and-pepper gray, dark gray, and black and white speckled. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
