Download Topic 1 Terms used to classify rocks and to describe rock properties

GEOLOGY 12
CHAPTER 3 IGNEOUS ROCKS
MAIN TOPIC QUESTIONS & ANSWERS
Topic 1
Terms used to classify rocks and to describe rock properties.
1)
elastic limit
The maximum stress that can be applied to a body without resulting in permanent
deformation - the rock reverts to its original shape after the stress is removed. In the
case of a fault or a fold the elastic limit is exceeded and the deformation becomes a
permanent structure of the rock. (see plastic deformation)
2)
glassy
An igneous rock without crystal structure that forms from very rapid cooling of
magma. The rapid cooling does not provide enough time for crystal growth.
3)
igneous
A rock formed by the crystallization of magma or lava.
4)
metamorphic
A rock that experienced alteration of the minerals, textures and composition caused
by exposure to heat, pressure and chemical actions.
5)
permeability
A measure of how well a material can transmit water. Materials such as gravel, that
transmit water quickly, have high values of permeability. Materials such as shale,
that transmit water poorly, have low values. Permeability is primarily determined by
the size of the pore spaces and their degree of interconnection.
6)
plastic deformation
Beyond the elastic limit the material undergoes plastic deformation. Unlike elastic
deformation, plastic deformation is not recoverable, i.e. the change is permanent.
7)
porosity
The volume of pore space in a rock, sediment or soil. Usually expressed as a
percentage. This pore space can include openings between grains, fracture
openings and caverns.
8)
rock cycle
All rock at or near Earth's surface is being modified by the processes of
metamorphism, melting, crystallization, lithification and weathering. These
processes move rock material through the states of metamorphic rock, igneous
rock, sedimentary rock, melts and sediment. The natural and continuous cycling of
rock materials through these states is known as the rock cycle.
9)
sedimentary
A rock formed from the accumulation and consolidation of sediment, usually in
layered deposits.
10)
strain
A change in the volume or shape of a rock mass in response to stress.
11)
tensile stress
Tensile stress is that type of stress in which the two sections of material on either
side of a stress plane tend to pull apart or elongate.
12)
thin sections (Topic 1* or 5)
used to microscopically examine minerals and textures in igneous rocks
Topic 2 Terms used to discuss the melting of rocks to form magmas.
13)
volatiles
dissolved water and gases in a magma; lowers melting temperatures of silicate
materials
14)
solid solutions
will melt at a temperature that is lower than the melting temperature of the pure
endmember compositions
15)
phase diagrams
used to show range of conditions winder which particular minerals, or mineral and
melt, are stable.
16)
partial melting
one way that magmas are formed; many magmas form from partial melting of the
upper mantle
Topic 3
Terms used to describe the crystallization of magmas.
17)
N.L. Bowen
recognized the sequence of crystallization of silicate minerals (Bowen's Reaction
Series)
18)
continuous reaction series
the plagioclase branch of Bowen's Reaction Series
19)
discontinuous reaction series
the ferromagnesian branch of Bowen's Reaction Series
Topic 4
Terms which represent three ways to alter the compositions of magmas.
20)
fractional crystallization
one way the composition of a magma can be changed
21)
assimilation
another way to change the composition of a magma by melting other rocks
22)
magma mixing
another way to change the composition of a magma by mixing two or more magmas
23)
felsic (Topic 3 or 4*)
describes compositions that are rich in silicon and poorer in magnesium and iron;
opposite of mafic
24)
mafic (Topic 3 or 4*)
describes compositions that are rich in iron and magnesium and poorer in silicon
Geology 12
Chapter 3 Main Topic Questions
Page 2
Topic 5
Terms used to describe (or observe) textures of igneous rocks.
25)
glassy
texture that lacks any obvious crystals
26)
vesicular
texture that shows holes or pockets left by gas bubbles
27)
groundmass
fine-grained crystals surrounding larger crystals in a porphyritic rock
28)
porphyritic
texture that show two distinct sizes of crystals
29)
phenocrysts
larger crystals in a porphyritic rock
30)
pegmatite
texture that has extremely large crystals
Topic 6 Terms used to describe characteristics of intrusive rock structures.
31)
country rock
The pre-existing rock that magma intrudes into. A Xenolith is a broken-off piece of
country rock that is floating in the magma and becomes part of the newly
crystallized pluton. (Add this term to your list for BONUS marks.)
32)
wallrock
same as country rock
33)
intrusions
general name for any body formed by magma crystallizing below the earth's surface
34)
fractures
cracks or openings that may control the shape of an intrusive body
35)
pluton
another generic name for any intrusive body
36)
concordant
a pluton that intrudes parallel to the structure of the country rock
37)
discordant
contact of the pluton cut across structure in the country rock; opposite of concordant
38)
chilled margins
sometimes form along the edges of a pluton where the magma cools more quickly
in contact with the country rock
Geology 12
Chapter 3 Main Topic Questions
Page 3