Answer :
Final answer:
Fossiliferous limestone is composed mainly of the mineral calcite (CaCO3) and is characterized by its softness, fine-grained texture, and presence of fossils. It forms in marine environments through the accumulation and solidification of the calcite-based remains of marine organisms.
Explanation:
Fossiliferous limestone is typically composed of a base mineral called calcite, which is a form of calcium carbonate (CaCO3). Calcite is soft and can easily be scratched with steel or a copper penny, contributing to the softness of limestone.
Distinctive properties of fossiliferous limestone include its ability to fizz in dilute hydrochloric (HCl) acid due to the presence of calcite, and the fact that it is commonly fine-grained and homogeneous. Additionally, the presence of fossils is a key characteristic, as fossils are common in this type of limestone.
The formation of fossiliferous limestone generally occurs in marine environments where creatures such as clams and corals, composed of CaCO3, die and their remains accumulate on the ocean floor. Over time, with the combination of pressure and chemical reactions, the calcite from these remains precipitates and solidifies to form limestone. This process can occur when CaCO3 in CO2-rich water rises towards the surface or when the water is heated, causing CO₂ to be released and CaCO3 to precipitate from the solution. Fossiliferous limestone layers may also contain other minerals like chert, which is hard silica that can weather to a brown color on the surface.
