Sedimentary Rocks Rocks that form by the compaction and cementation of sediment that transform sediment into solid rock are sedimentary.

Sedimentary Rocks Geologists estimate that sedimentary rocks account for only 5% (by volume) of the Earth’s outer 16 km but they make up 75% of the rocks exposed as outcrops at the surface of the Earth.

Lithification – the process of turning loose sediment into stone. 1.Compaction – as sediments accumulate through time, the weight of the overlying material compresses the deeper sediments until they harden. 2.Cementation – cementing material through time precipitate on to the sediment, filling the spaces and joining the particles, Calcite, silica and iron oxide are the most common cements.

Sedimentary rocks Sedimentary rocks There are two classes of sedimentary rocks. 1. Clastic (detrital) – formed by the lithification of sediment formed by weathering, erosion and mass wasting. Example - sandstone

2. Chemical sedimentary rocks – rocks that formed when soluble material dissolved in lakes or seas precipitates out and hardens. Example - gypsum

Classification of Sedimentary rocks Clastic rocks Clastic sedimentary rocks are classified by their grains size. Siltstone – gritty between the teeth Sandstone – feels like sand. Conglomerate –rounded thumbnail size and larger Breccia – angular thumbnail size and larger.

Chemical sedimentary (sometimes called precipitates or evaporites.) These rocks have a crystalline structure. Same shape, same color, same size crystals. (Note – These are not interlocking crystals like igneous rocks.) They can be called biochemical if they have organic material in it.

Identification Clues Sedimentary rocks can be found in layers. Example - sandstones. They are sometimes soft. example - gypsum.

Identification clues Continued They may contain fossils. Example – limestone They look like a broken rock stuck together. Example - conglomerate