Graywacke is a “dirty” sandstone distinguishable by its angular to subangular clasts and minor silt/mud content. It often hosts graded beds.
Rock group | Sedimentary |
Origin | Clastic/detrital |
Particle size (Wentworth) | 0.0625 – 2 mm |
Graywacke in Hand Sample
Silurian-aged graywacke (from Siccar Point!)
Ordovician-aged Martinsburg Formation graywacke
Turbidites from Patagonia
Graywacke in Thin Section
Graywacke, plane polars
Graywacke, crossed polars

Graywacke, Plane Polars
Graywacke in plane polarized light. Magnification: 40x Click here to see graywacke in crossed polars: https://youtu.be/z94ywQWuTNE Click here to explore a ha…

Graywacke, Crossed Polars
Graywacke in cross polarized light. Magnification: 40x Click here to see graywacke rotating in plane polars: https://youtu.be/af4VFMA-oAU Click here to explo…