Identification guide · Igneous Rocks
How to Identify Dacite
Dacite is typically light gray to tan and porphyritic, with visible plagioclase, quartz, or dark hornblende and biotite crystals scattered through a fine-grained to glassy groundmass. Overall hardness is close to that of its feldspar phenocrysts, around 6, so testing is best done on individual grains. It lacks the dark color and abundant iron-magnesium minerals of andesite and basalt. Dacite is easily confused with rhyolite and andesite, and distinguishing them often requires checking mineral content or silica percentage in a lab.
Dacite identification checklist
| Color | Gray, Light gray, Tan, Pale brown | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Dull to vitreous | 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 | Conchoidal to uneven | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 2.6–2.7 | Ordinary rock-like heft (specific gravity about 2.6500000000000004), similar to quartz. |
Extra tests for Dacite
Glass check. Dacite shares a glassy luster and conchoidal fracture with man-made glass. Glass sits near Mohs 5.5 and often contains round gas bubbles, so a hardness test and a hand lens separate them.
Dacite 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. Dacite vs Quartz →
Dacite is harder (Mohs 6–7) than Andesite (Mohs 5–6), so Dacite will scratch Andesite and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Dacite vs Andesite →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Dacite vs Rhyolite →
Both sit near Mohs 6–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Dacite identification FAQ
How can you tell if a rock is Dacite?
Check the color (gray, light gray, tan, and pale brown), the dull to vitreous luster, a Mohs hardness of 6–7. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Dacite?
Dacite 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 Dacite and Quartz?
Dacite (Mohs 6–7, dull to vitreous luster) and Quartz (Mohs 7, vitreous, greasy on fracture surfaces luster) look alike, but hardness, streak and heft usually separate them. See the full Dacite vs Quartz comparison for a side-by-side table.
Is Dacite worth anything?
Entry-level Dacite 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 Dacite?
Dacite is most often gray, light gray, tan, and pale brown. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
