Shale is the protolith of slate.
Rock group | Sedimentary |
Origin | Clastic/detrital |
Particle size Wentworth | ≤ 62.5 µm |
Special properties | Fissile; splits along bedding planes |
Shale in Hand Sample
Shale is often fossiliferous, frequently preserves sedimentary structures such as crossbedding and mudcracks, and comes in varying shades of grey, tan, black, green, and red.
Fossiliferous Millboro Formation shale from West Virginia
Mudcracks and raindrop impressions in a red shale
Graptolites in black shale
Shale in Thin Section
Laminated shale, plane polars
Laminated shale, crossed polars

Laminated Shale, Plane Polars
Laminated shale in plane polarized light. Magnification: 100x Click here to see laminated shale rotating in crossed polars: Click here to explore a hand samp…

Laminated Shale, Crossed Polars
Laminated shale in cross polarized light. Magnification: 100x Click here to see laminated shale rotating in plane polars: https://youtu.be/J8lp7IJaejk Click …

Oil shale, plane polars
Magnification: 40x Click here for crossed polars: https://youtu.be/ySkoEEiCNzI

Oil shale, crossed polars
Magnification: 40x Click here for plane polars: https://youtu.be/AJW4wmW39r8