Question

Sedimentary rocks are also known as secondary or derived rocks. Comment

Answer 1

they are known as because they are foormed from sediment

Answer 2

Most earth scientists I know prefer other terms such as “clastic” for sedimentary rocks that form by the consolidation of material derived by erosion of preexisting rocks, “chemical” for sedimentary rocks that result from the precipitation of minerals at or near the Earth’s surface (evaporites, calcareous cave deposits, some chert), and “biogenic” for rocks (marine limestone, some chert) formed dominantly by the remains of former organisms.

The label “secondary” is also ambiguous because, in older texts, eras were labelled “Primary (for Paleozoic), Secondary (for Mesozoic), Tertiary and Quaternary (for parts of the Cenozoic)”. These labels were used for the sedimentary rocks containing the appropriate index fossils, but they are now outdated.

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