The true statement among the options you provided is:
All sedimentary rocks contain weathered rock and sediment.
The other statements are not accurate:
- Stalagmites and stalactites are not sedimentary rocks; they are mineral formations typically made of calcium carbonate and are related to precipitation processes in caves, not directly classified as chemical sedimentary rocks.
- Peat and coal are considered organic sedimentary rocks, not clastic sedimentary rocks.
- Organic sedimentary rocks are primarily composed of the remains of plants and animals, not mineral crystals.