Ch. 6, p. 154: #3, 5, 6, 9, 11, 14

3.  What do mud cracks tell about the environment of deposition of a sedimentary rock?

They indicate an environment in which sediment got wet and then dried out.  Such an environment could be a flood plain, or tidal flat.

5.  List the clastic sediment particles in order of decreasing grain size.

boulder >256 mm
cobble  64-256 mm
pebble   2-64 mm
sand       1/16 - 2 mm
silt           1/256 - 1/16 mm
clay           < 1/256 mm

6.  How does a sedimentary breccia differ in appearance and origin from a conglomerate?

A breccia has angular fragments, whereas a conglomerate has rounded rounded fragments.  In each rock, the fragments are roughly the same size ("gravels").  A breccia suggests sediment that didn't travel far from its source.  A conglomerate formed from sediment that probaby traveled far from its source, giving it the opportunity to become rounded.

9.  What is the origin of coal?

Coal forms from the compaction of plant material that has not completely decayed (pg. 142).  Shallow swamps and bogs are typical environments.

11.  How do evaporites form?  Name two evaporites.

Evaporites form from crystals that precipitate during evaporation of water (water with dissolved material in it), such as in a drying lake bed.  Rock gypsum and rock salt are two evaporites.

14.  Explain two ways that cross-bedding can form.

Cross-bedding can form in a desert environment when sand dunes migrate.  Cross-bedding can also form in river channels when sand bars or ridges migrate downstream.

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