Geology Reference
In-Depth Information
Exercise 1 • Earth Materials, Geologic Time, and Geologic Processes
11
TABLE 1.7 Common Metamorphic Rocks
Texture
Rock Name
Diagnostic Characteristics
Foliated (coarse)
Alternating bands of unlike minerals, such as feldspar and quartz, with lesser
amounts of mica, and ferromagnesian minerals
Gneiss
Foliated (medium to fine)
Foliation due to parallel arrangement of platy minerals; mica, chlorite, talc,
hornblende, and garnet are common minerals
Schist
Foliated (very fine)
Quartz, muscovite, and chlorite are common minerals but are not visible with
the unaided eye; may resemble shale but has no earthy odor; compact and
brittle; varicolored. Generally represents metamorphosed shale.
Slate
Principally quartz; varicolored; very hard, massive. Original rock is generally
quartz rich sandstone.
Quartzite
Nonfoliated
Nonfoliated
Principally calcite or dolomite; crystals commonly large and interlocking;
varicolored. Original rocks are limestone and dolostone.
Marble
texture is characterized by an absence of an align-
ment of minerals due to the random orientation or
equidimensional nature of constituent minerals. The
common metamorphic rock characteristics are sum-
marized in Table
1.7.
In some cases, metamorphic rocks retain properties
of the original rock and, therefore, respond in the same
way as the original rock. This is especially true of mar-
ble, which should be subject to the same considera-
tions as limestone because of its high solubility.
Metamorphic rocks provide many economic
products including building stone, monument and
decorative stone, aggregate, and gemstones, as well as
fossil fuel (anthracite).
SIGNIFICANCE
The environmental significance of
metamorphic rocks is similar to that of igneous rocks
in that they are generally nonporous and
impermeable; they are, therefore, a poor source of
groundwater, and provide a firm foundation for
construction projects. However, one characteristic of
foliated metamorphic rocks that needs special
consideration is the direction of orientation of the
foliation or planes of schistocity. These may represent
planes of weakness that must be considered in
foundation support, excavations, and in any situation
where sliding may take place along these planes.
QUESTIONS 1, PART B3
1.
Your instructor will provide specimens of metamorphic
rocks for you to identify. Using the information presented in
Table 1.7, determine the texture, composition, and other
properties of each specimen to identify the metamorphic rock
and probable original rock. Record your observations in
Table 1.8.
