Final answer:
Dolostone is a type of carbonate sedimentary rock that forms by alteration of limestone by magnesium-rich fluids, unlike marble which is a metamorphic rock formed by the recrystallization of limestone due to heat and pressure.
Step-by-step explanation:
The correct answer to the statement about dolostone is that dolostone forms by alteration or replacement of limestone by magnesium-rich fluids. Dolostone is a type of sedimentary rock known as a carbonate rock that is chemically related to limestone but contains a higher percentage of the mineral dolomite, which is calcium magnesium carbonate.
In contrast to marble, which is a metamorphic rock formed from limestone through the process of metamorphism involving heat and pressure, dolostone's origins lie in the chemical alteration of limestone without the high degree of recrystallization that occurs in the formation of marble. Dolostone is not a clastic sedimentary rock, fine-grained evaporite, a result of increased seawater pressure, nor is it formed from plant material.