How to Identify Shale: What to Look For and Home Tests

Clastic sedimentary rocks are cemented grains of older rock: sand, silt or clay. Grain size is the first thing to judge, and layers, ripple marks or fossils confirm the sedimentary origin. The properties that identify Shale — cleavage or fracture: Splits into thin platy sheets; may feel slippery when wet. For a rock, texture and grain size matter more than any single hardness number.

• Grain test: shale is made of compacted clay or mud with extremely fine grains — the minerals generally cannot be identified by eye (or even under a microscope) without the aid of X-ray analysis.

• [Slate](/lookup/rocks-and-minerals/slate): Slate has a higher luster, is harder and denser, and splits more evenly along parallel foliation surfaces; shale splits less evenly and may feel slippery when wet.

Thick shale beds in eastern Colorado, and reddish-brown siltstone/mudstone in Owen Canyon.

Photograph a fresh, unweathered surface in daylight, then a second shot of any crystal faces or broken edge. Include a coin for scale. If you did a streak test, photograph the streak next to the specimen. The app suggests the likely mineral or rock; confirm with hardness and the tests above before you label it.