Final answer:
The reaction of fizzing when HCl is applied to rocks containing fossils typically indicates the presence of calcite, a common mineral in limestone that contains fossils. Limestone may also include chert, which does not fizz. The mineral composition of fossils, like calcite and apatite, can help identify if they are unaltered or if they have undergone processes like silicification.
Step-by-step explanation:
Fossils and Geological Reactions
The question describes a situation where abundant fossils and fossil fragments are cemented together in rock that fizzes upon exposure to hydrochloric acid (HCl). This reaction is indicative of the presence of calcite (CaCO₃), a mineral commonly found in limestone.
Limestone is known for containing fossils and can react with dilute acid to produce carbon dioxide gas, which is observed as a fizzing or effervescence. The fizzing helps to confirm that the main component of the rock is calcite. Some limestone may also contain harder minerals, such as chert, which does not fizz because it is primarily composed of silica.
The description of the fossils suggests they are unaltered, containing original minerals, such as calcite, that were biologically produced by the organisms when they were alive. These details help geologists and paleontologists in fossil identification and in understanding the conditions under which the fossil-bearing rocks formed.
Identifying the minerals within fossils is also vital for determining whether the fossil material is original or has undergone mineral replacement or recrystallization processes. For instance, minerals such as apatite, calcite, aragonite, and opal can be present in unaltered fossils, while the presence of minerals harder than glass and lacking acid reaction could point to the process of silicification, where silica replaces the original carbonate material in fossils.