Identification guide · Sedimentary Rocks
How to Identify Flint
Flint is typically dark gray, brown, or black on a freshly broken surface, often coated with a lighter, chalky white to tan cortex where it has weathered within or out of chalk, and it has a white streak consistent with its quartz composition. It shares chert's hardness of about 7 and dull to waxy luster, breaking with a smooth conchoidal fracture that produces sharp cutting edges, a quality exploited in flintknapping. Flint is essentially indistinguishable in composition from chert and jasper, and the terms are often used regionally rather than scientifically; flint specifically refers to the dark chert nodules found within chalk formations.
Flint identification checklist
| Color | Black, Dark gray, Brown | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Waxy to dull, glassy on fresh fracture | Compare a fresh surface with glass and metal; this luster is softer than either. |
| Transparency | Translucent at thin edges to opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 6.5–7 | It scratches glass and a steel knife and cannot be scratched by a steel file. |
| Fracture | Conchoidal | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 2.6–2.65 | Ordinary rock-like heft (specific gravity about 2.625), similar to quartz. |
Flint look-alikes and how to tell them apart
Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Flint vs Chert →
Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Flint vs Quartz →
Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Flint vs Smoky Quartz →
Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Flint identification FAQ
How can you tell if a rock is Flint?
Check the color (black, dark gray, and brown), the waxy to dull, glassy on fresh fracture luster, a Mohs hardness of 6.5–7. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Flint?
Flint has a Mohs hardness of 6.5–7. It scratches glass and a steel knife and cannot be scratched by a steel file.
What is the difference between Flint and Chert?
Flint (Mohs 6.5–7, waxy to dull, glassy on fresh fracture luster) and Chert (Mohs 6.5–7, waxy to dull luster) look alike, but hardness, streak and heft usually separate them. See the full Flint vs Chert comparison for a side-by-side table.
Is Flint worth anything?
Entry-level Flint 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 Flint?
Flint is most often black, dark gray, and brown. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
