Final answer:
The term a. 'spherical' is not a recognized type of sedimentary rock. Sedimentary rocks are classified as clastic, chemical, and biogenic; these types are based on their formation from weathering debris, chemical precipitation, or organic accumulation, respectively.
Step-by-step explanation:
The student has asked about which option is not a type of sedimentary rock. Sedimentary rocks are classified into different types based on their mode of formation and composition. These include clastic, chemical, and biogenic, also known as organic, sedimentary rocks.
Clastic sedimentary rocks are formed from mechanical weathering debris of other rocks. They are primarily classified based on grain size, and their composition includes minerals like quartz and feldspar. Chemical sedimentary rocks form through the evaporation of water which leaves behind minerals, and examples include rocks made of precipitated salt or limestone.
Biogenic or organic sedimentary rocks are composed of accumulated organic debris, from which coal, oil, and natural gas are derived.
Option 'a' which is spherical, does not fit into the standard classification of sedimentary rocks. Hence, 'a' spherical is not a recognized type of sedimentary rock and stands out as incorrect in this context.