RocksdayChert vs Flint
To tell Chert from Flint: Flint is the dark nodular form in chalk. In the US the name is also used loosely for tool-stone chert.
A hard sedimentary rock of microscopic quartz. Dark nodules in chalk are called flint.
Photo: Unknown, Public domain
Dark nodules of microcrystalline quartz, especially the ones that grew in chalk. In North America the word is also used for any chert that was knapped into tools.
Photo: Otis Crandell, CC BY-SA 3.0
Key differences
- Flint is the dark nodular form in chalk. In the US the name is also used loosely for tool-stone chert.
- Chert is the broader rock; flint is the dark nodular kind in chalk, though the names get swapped.
Side by side
| Property | Chert | Flint |
|---|---|---|
| Type | Sedimentary rock | Sedimentary rock |
| Mohs hardness | 6.5–7 | 6.5–7 |
| Luster | Waxy to dull | Waxy |
| Colors | Gray, Black, Brown, White | Black, Gray, Brown |
| Crystal system / structure | Microcrystalline quartz | Microcrystalline quartz nodules |
| Specific gravity | 2.5–2.7 | 2.5–2.7 |
| Found in | Flint Ridge, Ohio; Alibates, Texas | Chalk cliffs of southern England; Northern France |
Properties that are the same for both are grayed out.
How to identify chert
- Breaks with smooth, curved fractures and sharp edges.
- Waxy luster on fresh breaks.
- Scratches glass.
- Sparks when struck against steel.
Structure: Microcrystalline quartz
Full Chert guide →How to identify flint
- Dark gray to black nodules, often with a white chalky rind.
- Breaks in smooth curves with razor edges.
- Waxy on a fresh break, and it scratches glass.
- Sparks against steel.
Structure: Microcrystalline quartz nodules
Full Flint guide →More comparisons
Frequently asked questions
What is the difference between chert and flint?
Chert is a sedimentary rock with a Mohs hardness of about 6.5–7 and a waxy to dull luster, usually gray, black, brown or white. Flint is a sedimentary rock with a Mohs hardness of about 6.5–7 and a waxy luster, usually black, gray or brown.
How can you tell chert from flint?
Flint is the dark nodular form in chalk. In the US the name is also used loosely for tool-stone chert. Chert is the broader rock; flint is the dark nodular kind in chalk, though the names get swapped.
Could you tell them apart from a blurry close-up?
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