RocksdayChert vs Petrified Wood
How to tell them apart
A hard sedimentary rock of microscopic quartz. Dark nodules in chalk are called flint.
Photo: Unknown, Public domain
Ancient wood whose cells were replaced, one by one, with quartz — turning a tree into stone.
Photo: Michael Gäbler, CC BY 3.0
Key differences
- Chert has no wood structure.
Side by side
| Property | Chert | Petrified Wood |
|---|---|---|
| Type | Sedimentary rock | Fossil |
| Mohs hardness | 6.5–7 | 6.5–7 |
| Luster | Waxy to dull | Waxy to vitreous |
| Colors | Gray, Black, Brown, White | Brown, Red, Yellow, Gray, Black |
| Crystal system / structure | Microcrystalline quartz | Wood replaced by silica |
| Specific gravity | 2.5–2.7 | 2.6–2.9 |
| Found in | Flint Ridge, Ohio; Alibates, Texas | Petrified Forest, Arizona; Ginkgo Petrified Forest, Washington |
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 petrified wood
- Visible bark texture, growth rings or wood grain.
- Heavy and hard like agate.
- Colorful bands of red, yellow and brown in polished slices.
Structure: Wood replaced by silica
Full Petrified Wood guide →More comparisons
Could you tell them apart from a blurry close-up?
Play today's Rocksday