Which characteristic best distinguishes clastic sedimentary rocks from chemical sedimentary rocks in the field?

• A. A uniform mineral composition with no fragments
• B. Visible fragments and grain sizes present
• C. Rocks formed by precipitation and crystallization
• D. The rock consists of interlocking grains with no cement

Answer: (B)

In the field, the most reliable clue is whether you can see fragments or clasts within the rock. Clastic sedimentary rocks form from pieces of pre-existing rocks that have been weathered, transported, deposited, and cemented together, so they show visible fragments and a range of grain sizes. That texture—fragments of different sizes bound into a rock—is the telltale sign of a clastic sedimentary rock.

Chemical sedimentary rocks, on the other hand, originate when minerals precipitate from solution and crystallize, producing a crystalline or microcrystalline texture without distinct fragments. They often look more uniform and may appear as intergrown crystals rather than a mosaic of broken pieces.

So, the presence of visible fragments and varying grain sizes is the best field indicator that you’re looking at a clastic sedimentary rock.