Fossils in thin section
Corals in thin section
Aragonite or calcite fibers grouped into trabeculae; septa, tabulae and dissepiments are the internal plates used for classification. Rugose corals (solitary or colonial) show prominent vertical septa; tabulate corals are colonial with pronounced horizontal tabulae, like stacked floors.

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All fossil groups Carbonate classification
Sources
SEPM Strata: Skeletal Grains · Rygel & Quinton, Sedimentary Geology 9.7: Fossils in Thin Section