Geology Reference
In-Depth Information
Exercise 1 • Earth Materials, Geologic Time, and Geologic Processes
9
TABLE 1.4 Igneous Rock Identification
Sample
Number
Mineral
Composition
Other Identifying
Characteristics
Geologic, Environmental,
and Economic Significance
Texture
Name of Rock
TABLE 1.5 Sedimentary Rocks: Detrital (by granular texture*) and Chemical/Biochemical (by composition)
Conglomerate*
Rounded gravel-sized (>2 mm) rock and mineral fragments cemented together by silica (Si0
2
), calcite,
or iron oxides.
Sandstone*
Sand-sized (1/16 to 2 mm) particles of chiefly quartz cemented together by silica, calcite, or iron oxides.
Siltstone*
Silt-sized (1/256 to 1/16 mm) particles of rock fragments, quartz, and other minerals held together by
calcite, silica, or iron oxides or by a clay matrix.
Shale (mud-
stone)*
Clay-sized (< 1/256 mm) particles that are chiefly the product of weathering of feldspars and are lithified
by compaction. Mineral composition is chiefly clay minerals.
Limestone
A calcium carbonate rock, CaC0
3
, which may be formed by accumulation of fossil remains or chemical
precipitation from solution upon evaporation, it is composed of calcite and occurs in several varieties
including oolitic, fossiliferous, coquina, and chalk.
Dolostone
A calcium-magnesium carbonate rock, CaMg(C0
3
)
2
, composed largely of the mineral dolomite. Texture and
appearance are similar to limestone. Can usually be distinguished from limestone by its slow reaction to HCI.
Coal
An accumulation of vegetation that through compaction loses its water and volatile matter to become
relatively pure carbon. Peat and lignite are early stages of coal formation; bituminous coal represents a later
stage; anthracite is further transformed by heat and pressure and may be considered a metamorphic rock.
Rock gypsum
A chemical precipitate composed mainly of the mineral gypsum, CaS0
4
• 2H
2
0, which originates from evapo-
ration of lakes and seas in restricted bays and thus is an indicator of an arid climate at the time of formation.
Rock salt
(halite)
A chemical precipitate composed of the mineral halite, NaCI whose origin is similar to that of gypsum. A
significant physical property of rock salt is that it flows at relatively low temperature and pressure.
