ROCKS AND SOILS 



73 



TABLE 5.2 CLASSIFICATION Of SEDIMENTARY ROCKS 



Rock 



Origin 



Remarks 



Talus 



Breccia 



Soil 



Gravel 



Conglomerate 



Sand 



Sandstone 



Clay 



Loess 



Shale 



Chalk 



Marl 



Limestone 



Dolomitic limestone 



Till 



Tillite 



Diatomite 



Chert or cherty rocks 



Peat 



Lignite to coal 



Amber 



Petroleum 



Asphalt 



Tuff 



Phosphate rock 



Guano 



Gypsum 



Halite 



Limonite 



Hematite 



Fossils 



Concretions 



Geodes 



Veins 



Rock weathering 



Talus 



Rock weathering 



Rock weathering 



Gravel 



Rock weathering 



Sand 



Rock weathering 



Rock weathering 



Clay or loess 



Calcium carbonate 



Calcium carbonate and clay 



Chalk or marl 



Dolomite plus impurities 



Glaciation 



Till 



Diatoms 



Silica deposits 



Plants, usually sphagnum moss 



Peat 



Conifer gum 



Organisms 



Organisms 



Volcanic ash 



Animals or igneous rocks 



Animals 



Calcium sulfate 



Sodium chloride 



Iron solution 



Iron solution 



Organism remains 



Altered material 



Growth in a cavity 



Deposition 



Coarse angular fragments 



Cemented 



Unsorted material plus humus 



Coarse fragments rounded by wind and water 



Cemented 



Finer wind or water deposits 



Cemented 



Finest material deposited by water 



Finest material deposited by wind 



Cemented 



Soft, generally porous and fossiliferous 



Soft, generally porous and fossiliferous 



Further compacted and cemented 



Compacted and cemented 



Unsorted material 



Cemented 



Compacted silica shells of microscopic algae 



Impurities affect silica color and glassiness 



Decay and compaction 



Progressive compaction 



Fossilized resins 



Hydrocarbon remains 



Hydrocarbon remains 



Weathered and cemented 



Deposited, compacted, and cemented 



Wastes and remains 



Dehydration; a mineral 



Dehydration; table salt; a mineral 



Dehydration; yellow ochre 



Dehydration; red ochre 



Preserved, cast, etc.; often in limestone 



Solid, variable foreign rocks in a stratum 



Crystals within a hollow rock 



Materials filling cracks in strata 



so strong that any further breaks will not occur along 

 the original partings. 



SEDIMENTARY ROCKS 



Table 5.2 summarizes the common types of sedi- 

 mentary rocks and their diagnostic features. 



METAMORPHIC ROCKS 



Metamorphic rocks are formed when any kind of 

 rock is altered by pressure, temperature, and/or 

 chemical changes associated with commonly occur- 

 ring geological processes. These geological processes 



can be grouped into four types of metamorphism: 

 contact, regional, replacement, and geothermal. 

 Contacl metamorphism, also called igneous, is caused 

 by the extreme temperature and pressure of magma. 

 In such metamorphism the greatest change in rocks 

 occurs at the point of contact betvi^een the magma 

 and adjacent rocks. Regional {dynamic or kinetic) 

 metamorphism, like contact, is also brought about by 

 temperature and pressure, but as a result of folding of 

 the outer portion of the earth's crust. Replacement 

 or hydrothermal metamorphism is caused by chemical 

 changes triggered by superheated waters and their 

 chemicals, (•eothermal metamorphism is another tem- 

 perature-pressure process, but the metamorphic con- 



