Punjab PSC Exam: Identification of Sedimentary Rocks

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HardnessGrain SizeCompositionOtherRock Type
hardcoarseclean quartzwhite to brownSandstone
hardcoarsequartz and feldsparusually very coarseArkose
hard or softmixedmixed sediment with rock grains and claygray or dark and “dirty”Wacke/Graywacke
hard or softmixedmixed rocks and sedimentround rocks in finer sediment matrixConglomerate
hard or softmixedmixed rocks and sedimentsharp pieces in finer sediment matrixBreccia
hardfinevery fine sand; no clayfeels gritty on teethSiltstone
hardfinechalcedonyno fizzing with acidChert
softfineclay mineralsfoliatedShale
softfinecarbonblack; burns with tarry smokeCoal
softfinecalcitefizzes with acidLimestone
softcoarse or finedolomitefizzing with acid unless powderedDolomite rock
softcoarsefossil shellsmostly piecesCoquina
very softcoarsehalitesalt tasteRock Salt
very softcoarsegypsumwhite or pinkGypsum

Sedimentary rocks are the second great rock class. Whereas igneous rocks are born hot, sedimentary rocks are born cool at the Earth՚s surface, mostly under water. They usually consist of layers or strata, hence they are also called stratified rocks. Depending on what they՚re made of, sedimentary rocks fall into one of three types.