Fissility is the result of sedimentary or metamorphic processes. Planes of weakness are developed in sedimentary rocks such as shale or mudstone by clay particles aligning during compaction. Planes of weakness are developed in metamorphic rocks by the recrystallization and growth of micaceous minerals.

Why is shale The most common sedimentary rock?

The most common sedimentary rock is shale. It is made of compressed mud--that is, a mixture of clay and silt (fine particles of mineral matter). Shale is used in making bricks. Limestone, another common sedimentary rock, is made chiefly of the mineral calcite.

Why are Mudrocks most abundant?

Most mudrocks form in oceans or lakes, because these environments provide the quiet waters necessary for deposition. Although mudrocks can be found in every depositional environment on Earth, the majority are found in lakes and oceans.