Identification guide · Metamorphic Rocks
How to Identify Metaconglomerate
Metaconglomerate is usually gray, white, and tan with a dull luster and is opaque. It has a Mohs hardness of 6.5. It scratches glass and a steel knife and cannot be scratched by a steel file. Its streak is variable by pebbles and matrix. It is most often confused with Conglomerate, Hematite, and Amphibolite; the tests below separate them.
Metaconglomerate identification checklist
| Color | Gray, White, Tan, Red, Brown, Black | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Dull | Compare a fresh surface with glass and metal; this luster is softer than either. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 6.5 | It scratches glass and a steel knife and cannot be scratched by a steel file. |
| Streak | Variable by pebbles and matrix | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Variable; may show foliation in matrix | |
| Fracture | Granular to uneven | |
| Specific gravity | 2.65 | Ordinary rock-like heft (specific gravity about 2.65), similar to quartz. |
Metaconglomerate look-alikes and how to tell them apart
Metaconglomerate is harder (Mohs 6.5) than Conglomerate (Mohs 3–7), so Metaconglomerate will scratch Conglomerate and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Metaconglomerate vs Conglomerate →
Both sit near Mohs 6.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Metaconglomerate vs Hematite →
Metaconglomerate is harder (Mohs 6.5) than Amphibolite (Mohs 5.5), so Metaconglomerate will scratch Amphibolite 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. Metaconglomerate vs Amphibolite →
Both sit near Mohs 6.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Metaconglomerate vs Hornfels →
Field tips
- Look for rounded pebbles or cobbles inside a hard recrystallized matrix.
- Flattened, stretched, or lens-shaped pebbles support metamorphic deformation.
- Metaconglomerate is usually harder and more recrystallized than ordinary conglomerate.
- Photograph both the whole specimen and close-up pebble-matrix contacts.
Metaconglomerate identification FAQ
How can you tell if a rock is Metaconglomerate?
Check the color (gray, white, tan, and red), the dull luster, a Mohs hardness of 6.5 and a variable by pebbles and matrix streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Metaconglomerate?
Metaconglomerate has a Mohs hardness of 6.5. It scratches glass and a steel knife and cannot be scratched by a steel file.
What is the difference between Metaconglomerate and Conglomerate?
Metaconglomerate (Mohs 6.5, dull luster) and Conglomerate (Mohs 3–7, variable; dull matrix to vitreous clasts luster) look alike, but hardness, streak and heft usually separate them. See the full Metaconglomerate vs Conglomerate comparison for a side-by-side table.
Is Metaconglomerate worth anything?
Entry-level Metaconglomerate 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 Metaconglomerate?
Metaconglomerate is most often gray, white, tan, and red. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
