Which sedimentary rocks are formed from mostly organic matter?
=== limestone commonly forms from the accumulation of calcium carbonate by various marine animals; coal is a carbon-rich compaction of plant material which was not allowed to break down in the presence of air … rock salt and rock gypsum are compacted and lithified evaporites (formed by precipitating out of evaporating water); sandstone and shale are compacted and lithified products of rock weathering, transport and deposition (don’t let lithified concern you – it’s just a fancy word meaning “made into rock”); conglomerate is a generic term for natural concrete – a mixture of pebbles, sands, and clays, compressed into a rock; dolostone is a chemically altered limestone, where some of the calcium has been replaced with magnesium … I’d go with 2.
