Here's a breakdown of the size range:

* Clay minerals: Less than 0.0039 mm (4 micrometers) in diameter

* Silt: Between 0.0039 mm (4 micrometers) and 0.0625 mm (62.5 micrometers) in diameter

The very small size of these particles is what gives shale its characteristic fine-grained, layered texture and often splits easily into thin sheets.

Additionally, shale may contain small amounts of other materials like:

* Quartz

* Feldspar

* Carbonates

* Organic matter

These can be present as larger fragments, but the overall composition is dominated by the very fine-grained clay and silt.