Rock Cycle - Rocks (5B)

  • Examining different sedimentary rocks.
  • Discussing environments of sedimentary deposition.
  • chert
  • conglomerate
  • diatomite
  • limestone
  • mudstone
  • sand
  • sandstone

Students examine sedimentary rocks.

Russian River in Northern California brings sediment to the coast. 


Sedimentary rocks form at the Earth’s surface from clastic material (pieces of other rocks or fragments of skeletons) which have become cemented together, and by chemical mechanisms including precipitation and evaporation.

There are many environments associated with sedimentary rock formation, including oceans, lakes, deserts, rivers, beaches, and glaciers. The diagram shows several important sedimentary rock forming environments:

EOLIAN - Eolian refers sediment erosion, transportation, and deposition by wind. Eolian environments are particularly common in deserts. Sand dunes are an excellent example of an eolian feature.

ALLUVIAL FAN - Alluvium is the cover of soil, sand, and fine grained rocks on the Earth’s surface. An alluvial fan is a large fan-shaped pile of alluvium, deposited by a combination of stream and landslide processes.

GLACIER - As they flow downhill, glaciers carry lots of loose rock and debris. This material acts like sandpaper, and cuts away at the underlying rock. Glacial sediment is deposited as the ice melts. Students may not realize the power of glaciers.

FLUVIAL - Fluvial refers river environments. Water is very efficient at eroding and transporting sediment. You may want to show students pictures of different types of rivers.

DELTA - a delta is the sediment deposit that forms at the mouth or a river, where it enters a lake or the ocean. Sediment is deposited as the water slows down, producing an underwater fan shaped deposit.

  1. Point out different sedimentary rock forming environments to the students. Emphasize there are many environments in which sedimentary rocks are formed, and that is why sedimentary rocks are very common on the surface of the Earth.
  2. Go over the rock specimens before the students examine them. This will help guide each student’s observational skills on the key characteristics of each rock. Encourage them to use a hand lens or microscope. In your review, point out the following:

    CLASTIC SEDIMENTARY ROCKS - In general, produced from broken particles that have been cemented together.

    SAND: particles are separate, no cement

    SANDSTONE: sand size particles that are cemented together; individual grains are visible.

    DIATOMITE: very small particles that are cemented together. These are diatoms (one celled marine plant) and radiolarians (marine protozoans). They are visible only with special microscope slides.

    CONGLOMERATE: larger particles (pebble- or gravel- sized) that are cemented together, coarse grained

    MUDSTONE: very small particles cemented together, with no biological ingredients, fine grained

    CHEMICALLY DERIVED - Composed of precipitated minerals, which grew out of water.

    CHERT: red, hard, very fine-grained, cannot see any particles.

    LIMESTONE: fizzes with dilute HCl, hard, generally cannot see particles, although composed of fossils

  3. Have the students look at the rocks above. The students should notice that the chemically produced rocks do not resemble the other sedimentary rocks. Conclude with the students that sedimentary rocks are sometimes easy to interpret, sometimes not!

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