Question

Sandstone and Shale are examples of which category of sedimentary rocks?

• A. Chemical
• B. Biochemical
• C. Organic
• D. Mechanical

Answer 1

Answer:

D. Mechanical

Sedimentary Rocks Classification

Mechanical Sedimentary Rocks (Clastic Rocks)

• These rocks are formed from the accumulation and cementation of mineral and rock fragments (clasts) that have been weathered and eroded from pre-existing rocks.

• The fragments are transported by wind, water, or ice and deposited in layers.

• Sandstone is a prime example, composed primarily of sand-sized mineral grains or rock fragments, most commonly quartz. It forms from the lithification of sand.

• Shale is another key example, formed from compacted clay-rich or silty sediment. It is characterized by its fine grain size and fissility (tendency to split into thin layers).

• Other examples of mechanical sedimentary rocks include conglomerate (rounded pebbles), breccia (angular fragments), and siltstone (silt-sized grains).

Formation Process

• Weathering: The breakdown of existing rocks into smaller pieces.

• Erosion: The transport of these fragments by natural agents.

• Deposition: The settling and accumulation of transported sediments.

• Compaction: The weight of overlying sediments reduces pore space.

• Cementation: Minerals dissolved in groundwater precipitate in the pore spaces, binding the sediments together into solid rock. Common cementing agents include silica, calcite, and iron oxides.