Mass of the shells will remain constant.
Step-by-step explanation:
Sedimentary rocks are formed by the rocks that have been weathered. The microscopic shells, small pieces of rocks and mineral particles get deposited on this weathered sedimentary rocks.
The texture or chemical properties of the microscopic shell get changed. but the amount of microscopic shell deposited to make sedimentary rocks remains the same.
Chalk and coral reefs are the example of sedimentary rocks made up with microscopic shells.
The skeletal part of the shells takes part in rock formation whose mass remains unchanged although physical and chemical properties go changes.