Lab5-MetamorphicRockIDIntroInfo12.pptx

Metamorphic Rock Identification
Texture – The term texture refers to the size, shape, and orientation of the minerals, particles, and other substances that make up a rock. There are two major textural groups in metamorphic rocks:
Foliated – In this texture the mineral crystals in the rock are aligned with each other. This alignment may be displayed as parallel planes along which the rock splits, by overlapping sheets of platy minerals such as micas and chlorite, or by alternating layers of light and dark minerals.
Foliated texture is further subdivided based on the presence or absence of pronounced color banding in the rock. Rocks without distinct alternating bands of light and dark minerals are described a non-color banded, whereas rocks with alternating bands of dark and light minerals are described as color banded.
Color banding is also referred to as gneissic foliation.
Foliated textures are further described based on the grain (crystal) size in the rock.
Examples of complete descriptions of foliated metamorphic rocks include:
“foliated, non-color banded, very fine grained” for slate,
“foliated, color banded, coarse grained” for gneiss, and
“foliated, non-color banded, fine grained” for phyllite.
Nonfoliated – In this texture the mineral crystals in the rock have grown in many directions and most do not show alignment. As a result, nonfoliated rocks commonly appear massive and structureless with only a few lines of impurities through the rock.
These rocks may break across, rather than around, mineral grains to produce a scaly surface on the specimen.
Nonfoliated textures are further described on the basis of the grain (crystal) size in the rock.
Examples of complete descriptions of nonfoliated metamorphic rocks include:
“nonfoliated, medium grained” for a quartzite, and
“nonfoliated, coarse grained” for marble, or alternatively
“nonfoliated, medium grained” for marble

Composition – Indicate the mineral composition of the rock based on observations with a hand lens and, if needed, physical or chemical tests. Identify and list all visible minerals present, including the color of each mineral.
 
Rock Name – Use the Classification of Metamorphic Rocks chart to determine the name for each of the rocks.
For schists, include the dominant or distinctive visible mineral.
Examples of some of the names given to schists include garnet schist, chlorite schist, biotite schist, and muscovite schist.
Probable Parent Rock(s) – All metamorphic rocks are formed by the action of heat and/or pressure on pre-existing igneous, sedimentary, or metamorphic rocks. The pre-existing rock is called either the parent rock or the protolith.
Refer to table 6.1 on page 140 of your textbook and to Section 7.3.1 in your laboratory manual for parent rock(s).
Indicate the name(s) of the probable parent rock(s) in last column of the metamorphic rock identification form.
For serpentinite, the parent rock(s) are typically ultramafic rocks such as peridotite.

Be as accurate and complete as possible in your work. Please ask questions when you have them. You are encouraged to work with your classmates on identifying the rocks, but the observations and wording of your answers on the Metamorphic Rock Identification Form should be your own.

You may find the Recognition of Metamorphic Rock Textures flow chart useful in identifying textures in metamorphic rocks.