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1) Igneous are derived from the hardening of
molten magma (intrusive or volcanic, with felsic,
intermediate, and mafic varieties)
2) Sedimentary are derived from detrital or
chemical sediment, the products of mechanical
and chemical weathering and chemical
precipitation.
3) Metamorphic are the result of burial,
increasing temperature and pressure, and fluid
transfer processes during recrystallization
(low, medium, and high grade)
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
• Igneous rock forms when hot magma cools and solidifies. Sedimentary rocks form when
sediment is compacted and cemented together (lithified), or when minerals precipitate from
solutions. Mechanical weathering and physical breakdown of a parent material (usually rock)
produces clastic or detrital sediment, whereas chemical sediment is accreted through
biological processes or precipitates directly from hydrothermal or briny waters. Metamorphic
rocks are compacted, heated, pressurized, and altered from burial, thermal contact, and fluid
transfer during recrystallization and alteration.
Laboratory 3. Igneous Rocks
• Rocks are identified by their colors, textures, and other physical properties like
hardness, weight (density or specific gravity), magnetism (magnetite), and
reactivity with acids (limestone and marble).
• The first exercise for this lab is to study and become familiar with 12 igneous rock
specimens included in a Ward’s scientific rock kit, differentiating between those
of plutonic (intrusive) and volcanic (extrusive) origin.
• A secondary exercise will be to examine the loose sample of igneous rocks held by
RVCC, discuss them among your peers and professor, and categorize them.
• A third exercise will be to complete a puzzle depicting an ordered sequence of
igneous rocks exposed in a mountainside using knowledge about the geological
progression of igneous intrusions.
• By the end of this lab you should have a working familiarity with the principal
types of igneous rocks, have identified the most common rock-forming minerals
in the specimens, and seen the textures commonly found in the mafic,
intermediate, and felsic rocks.32
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
33
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
PLUTONIC
(intrusive varieties)Laboratory 3. Igneous Rocks
+1 os
+2 os
os – oxidation state
An element having a
+2 os (or charge) has
a higher electron
affinity because it has
twice the charge than
one with a +1 os.
• Calcium and magnesium (+2) are proportionately more abundant in mafic rocks
that crystallize form magma first with slow cooling and crystal growth.
•Parent magma composition largely determines the composition of igneous
rocks but a single magma can, however, yield different rock types.
34
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
Laboratory 3. Igneous Rocks
Texture in igneous rocks is related to cooling history; the slower the
magma cools, the more coarse-grained the rock becomes.
35
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
Laboratory 3. Igneous Rocks
•Typically, the coarsest-grained rocks formed in deep crustal chambers after rising out of the
mantle where it can accumulate and pond at the base of the crust or in the crust, or deep in
the roots of crustal mountain where rocks begin to melt from burial and heat. They become
exposed at the surface Eons after formation from crustal tectonics.
36
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
Laboratory 3. Igneous Rocks
37
Exercise 1.
An Igneous Rock
Collection by
Ward’s Scientific
Basalt
Diorite
Gabbro
Granite
Obsidian
Pegmatite
Peridotite
Pumice
Rhyolite (2)
Scoria
Syenite
38
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
Laboratory 3. Igneous Rocks
39
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
NOTES: NOTES:
Laboratory 3. Igneous Rocks
40
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
NOTES:
Laboratory 3. Igneous Rocks
41
Granite (Felsic)
Diorite (Intermediate)
Gabbro-Basic
RVCC loose
plutonic
material
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
Laboratory 3. Igneous Rocks
42
Rhyolite (Felsic)
Basalt-basic
Scoria
RVCC loose volcanic material
obsidian
Andesite (Intermediate)
Volcanic
bomb
Tuff
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
Laboratory 3. Igneous Rocks
_____ SS - red sandstone _______ B - basalt dike leading to basalt flow ______ D - diorite stock and sills
______Gr – granite ________ Pg – pegmatite ______ Gb – Gabbro 43
RVCC GEOL 157 Introduction to Geology Lab Manual GCH 2018-01
Laboratory 3. Igneous Rocks
44
Exercise 1.
An Igneous Rock
Collection by
Ward’s Scientific
1.Obsidian
2. Pumice
3. Scoria
4.Basalt
5. Rhyolite
6. Rhyolite
7. Granite
8. pegmatite
9. Andesite
10. Diorite
11. Gabbro
12. Peridotite