23. Sedimentary and Metamorphic Rocks

Photo 40: Limestone (Tyndall) with a marine life corpse in the rock. CIBC bank building, Edmonton, Alberta. 2011-05-10

Sedimentary Rocks

Sedimentary rock often start its existence as sand or gravel in a lake, river, or desert. Sedimentum is Latin for ‘settling.’ These fine rocks result from erosion and transportation. Sedimentary rocks come together during river deposition and later compaction (lithification) of the sediment. During compaction, the rocks and grains are tightly squeezed together. Water often runs through this material, depositing small amounts of silica and calcite. This is the process of cementation. Clastic sedimentary rocks are made up of all kinds of other rocks and rock material and encompass most of the sedimentary rock. Nonclastic sedimentary rocks are made up of organic deposition or from chemical solutions due to deposition and evaporation. Examples of sedimentary rock include: limestone (photo 40), shale, and sandstone (photo 41).

Photo 41: Loose sandstone used for cat litter, Drumheller, Alberta. 2011-05-12

Metamorphic Rocks

Metamorphic rock has been altered by heat and pressure. Metamorphic comes from a Greek word which means ‘change.’ Both Igneous and Sedimentary rocks can be melted and become metamorphic rocks. This melting happens during a comet impact or volcano eruption. One way of melting happens when lava flows out over other rocks during contact metamorphism. Some examples for metamorphic rocks are quartzite (quartz grains and silica cement), marble (from limestone) (photo 42), slate (from shale), gneiss (from granite), and schist.

Photo 42: Light coloured marble on the Toronto Dominion Bank Building during rock-walk in Edmonton, Alberta. 2011-05-10