Rock Topics

Composition of Sedimentary Rocks (Part 2)

Clay Minerals

Clay minerals usually form fine-grained rocks like this shale.  Clay minerals are a group of flaky silicate minerals that form from the weathering of pre-existing rocks and minerals.  Clay is the single most abundant type of sediment.

Shale (Photograph by Parvinder Sethi)


Dolomite forms the rock dolostone.  It forms when some of the calcium in calcite is replaced by magnesium.  The large white crystals on this sample are dolomite.  The entire rock is dolostone.

Dolomite (Photograph by Parvinder Sethi)