Answer :
Final answer:
Oolitic limestones are formed primarily through an inorganic process where calcium carbonate precipitates around nuclei in supersaturated water. In contrast, other options like chalk and coals involve organic processes, indicating their biological origin. Understanding these distinctions helps clarify the types of sedimentary rocks and their formation processes.
Explanation:
Understanding Inorganic Processes in Sedimentary Rock Formation
In sedimentary geology, various rocks are formed through inorganic processes, which primarily involve the precipitation of minerals from water. Among the types listed in the question, oolitic limestones are notable for being formed almost entirely through inorganic means. Here’s how that happens:
- Oolites: These are small, spherical grains made up of concentric layers of calcite. They form when calcium carbonate precipitates around a nucleus, such as a sand grain, in supersaturated water. This process is often facilitated by evaporation, creating conditions conducive for the precipitation of calcite.
- Chalk: While classified as a limestone, chalk originates from the accumulation of microscopic shells from organisms like coccolithophores and thus is not strictly inorganic.
- Calcic Sandstones: These are typically formed by the compaction and cementation of sand grains that contain calcite cement but do not directly precipitate from a solution.
- Coals: These are organic sedimentary rocks formed from the accumulation and alteration of plant material, so they do not fit the inorganic criteria.
- Fossiliferous Limestones: This type of limestone is rich in fossils, indicating a significant biological component in its formation.
In contrast, oolitic limestones serve as a clear example of rocks resulting from inorganic precipitation, emphasizing the diverse processes at play in sedimentary rock formation.
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