Download Lab 2-Igneous and Metamorphic rocks

Lab 2- Igneous & Metamorphic Rocks Name _________KEY_________________________
Section ______________________
Igneous Rocks
1. Complete the table below (the gray spaces) so it contains the necessary information for describing
igneous rocks. The table below should have the appropriate textural terms for each of the igneous
rock types. You should note that TEXTURAL terms apply ONLY to the specific category of rock to
which they belong. For example, the textural terms for igneous rocks are NOT to be used to describe
metamorphic or sedimentary rocks, or vice versa.
Igneous
Texture terms
Physical
description
Multicolored
Able to see
mineral crystals?

Phaneritic or
Coarse
grained
Not able to see
mineral crystals?

Aphanitic or
Fine grained
Lightly speckled
or uniform color
Mineral crystals
have two distinct
sizes? 
Porphyritic or
Mixed large &
small grains
Pieces look clastic
rather than
crystalline? 
Pyroclastic
What color is the
groundmass
(matrix)? The
phenocrysts?
Lightly speckled
or uniform color
Uniform color
Minerals
Probable EOF
What minerals are
present and in
what relative
amount?
What is the
overall rock
color? Is it light
or dark?
What minerals are
present and in
what relative
amount?
What color size
and shape are the
pieces?
Intrusive
Extrusive
Complex
Extrusive
2. What Textural classification term is given EXCLUSIVELY and ONLY TO igneous rocks with
visible mineral grains?_____________Phaneritic________________
3. What Textural classification term is given EXCLUSIVELY and ONLY TO igneous rocks with
mineral grains that are too small to identify the minerals by name?
___________________Aphanitic______________
4. What Textural classification term is given EXCLUSIVELY and ONLY TO igneous rocks with two
distinct sizes of mineral grains, one big and one small?
__________________Porphyritic___________
5. What Textural classification term is given EXCLUSIVELY and ONLY TO igneous rocks with
fragments that look like sediments that have been fused?___________Pyroclastic___________
Fall 2016
Felsic
2
1, 4, 8,13
Complex (both)
2*, 6
Extrusive
Intrusive
12
3
9, 10, 11
7
5
Mafic
Intermediate
6. In the circle above, place the NUMBERS of the rock samples in the appropriate igneous
composition category and according to which environment it would have formed in. Be sure to think
about what you see when you examine the rock to determine this. You should find the table you
completed in question #1 to be useful.
Fall 2016
Phaneritic (Porphyritic)
Phaneritic
Porphyritic
Porphyritic
Phaneritic
Aphanitic
Aphanitic
Aphanitic
Porphyritic
Aphanitic Glassy
Phaneritic
Aphanitic
2
3
4
5
6
7
8
9
10
11
12
13
Fall 2016
Aphanitic
TEXTURE
1
ROCK
#
Orthoclase; Quartz; Mica
Plagioclase;; biotite hornblende
Too small to be seen
Augite; Olivine; Plagioclase
F
I
M/I
M
Pumice
Diorite
Obsidian
Basalt
Scoria (Basalt)
M
Augite; Olivine; Plagioclase
Tuff (Rhyolitic)
F
Orthoclase; Quartz; Mica;
hornblende
Andesite
Granite
I
F
Orthoclase; Quartz; Mica;
hornblende
Basalt Porphyry
Rhyolite
Gabbro
Granite (porphyry)
Rhyolite
ROCK NAME
Plagioclase; Hornblende; Augite
M
F
M
F
F
Augite; Olivine; Plagioclase
Orthoclase; Quartz; Mica
Augite; Olivine; Plagioclase
Orthoclase; Quartz; Mica
Orthoclase; Quartz;
VISIBLE MINERALS
MAGMA
TYPE
(F,I,M)
7. Complete the table below for each of the igneous rocks samples provided.
Rapid (extrusive)
Intrusive
Extrusive
Extrusive
Rapid (extrusive)
Extrusive/explosive
Extrusive
Intrusive
Complex/extrusive
Extrusive)
Intrusive
Complex Intrusive
Extrusive
COOLING
HISTORY
3
Classification of Igneous Rocks
Igneous rocks are classified based on texture and mineral characteristics (also called
composition). The texture of an igneous rock describes its overall appearance based on the size,
shape and arrangement of its interlocking crystals. It depends on the origin of the rock, the
environment in which it formed, and many times on its composition. By knowing how to identify
the texture of an igneous rock, you can interpret local and sometimes regional geology while in the
field without sophisticated equipment.
Textures:
• Phaneritic (coarse-grained): most of the interlocking crystals are visible to the naked eye
and identifiable. Crystals present and easily viewed.
• Aphanitic (fine-grained): most of the interlocking crystals are not visible to the naked eye,
but some cleavage surfaces can be seen when tilting the rock back and forth in the light.
They will be about the size of a piece of glitter. Crystals present but often too small to see.
• Porphyritic: a mix of the above two. Some crystals will be easily seen (phenocrysts) while
others are not (groundmass). In a chocolate chip cookie, the phenocrysts are the chips, while
the rest of the cookie is the groundmass. Crystals present in both groundmass and
phenocrysts.
• Vesicular: some volcanic rocks look frothy or foamy, or bubbly. Small crystals are
sometimes present, sometimes not.
• Glassy: some volcanic rocks look like glass. No crystals present.
• Pyroclastic (fragmental): certain volcanic rocks look like they have bits and chunks of rock
fragments and ash, and will feel crumbly. No crystals present.
• Pegmatitic: crystals are usually huge (usually grater than 2 inches in size.
A useful figure relating textures and physical characteristics of igneous rocks
Metamorphic Rocks
8. The first part of this exercise is to finish filling out the table below (the gray spaces) so it
contains the necessary information for describing what you see in the rocks. The table below
should have the appropriate textural terms for each of the rock types. You should note that terms
apply only to the specific category of rock to which they belong. For example, the textural terms
for metamorphic rocks are not to be used with igneous or sedimentary rocks.
Metamorphic
Texture terms
Able to see layering
or banding? -
Foliated
No apparent layering Non -foliated
or banding? 
Fall 2016
Questions to
ask
Are grains
visible?
Subcategories Mineral visibility
What minerals
are present?
How distinctive
are the layers?
Is it
monomineralic?
Is it hard or
soft?
phyllitic
slatey
schistose
gneissic
Hard/no
Rxn=
Quartzite;
Soft/Rxn=ma
rble
No mineral grains
visible; layering is very
thin; dark colored
Few visible; small
Most visible; small to
medium
Easily visible; coarse
Does it react to acid?
9. Look at the minerals present in the samples of metamorphic rocks and place them in the
appropriate parent rock category (the circles) and the appropriate metamorphic grade
Sedimentary
3,4,5,7*,8*,9,10*,12,14*
1*,2,7,8*,10*
High Grade
Intermediate
Grade
Igneous
1*
14*
3,4,6,7*,8*,10*,11,13, 15
Low Grade
Fall 2016
FOLITATED
TEXTURE?
(Y OR N)
yes
yes
yes
no
yes
yes
no
no
yes
no
yes
yes
yes
yes
no
#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Galena, pyrite; quartz
Hornblende; garnet; micas (biotite
and muscovite)
None visible
Garnet; biotite, hornblende
None visible
calcite
Muscovite, garnet (red and green)
Quartz
Quartz
None visible
Quartz; Muscovite; garnet;
biotite
Quartz/Chert pebbles
None visible; mica sheen
Quartz; hornblende; augite
Quartz; hornblende; augite
MINERALS
Observed in rock specimens
low
high-intermediate
low
high-intermediate
low
variable
high-intermediate
variable
variable
low
high-intermediate
variable
low-intermediate
high
v high
METAMORPHIC
GRADE
(high, med, low)
Hydrothermal
Amphibolite Schist
Hornfels
Blueschist
Red Slate
Marble
Garnet Schist (Phyllite)
Quartzite (green)
Quartzite (pink)
Black slate
Mica Schist
Metaconglomerate
Phyllite
Gneiss
Migmatite
ROCK NAME
10. Complete the table below for each of the samples that you have determined to be metamorphic rocks
sandstone
basalt
shale/siltstone
volcanics/shale
shale
limestone
shale
arenite (sandstone)
arenite (sandstone)
shale
shale
conglomerate
shale
shale
shale
PARENT
ROCK
Classification of Metamorphic rocks
Metamorphic rocks are grouped by their texture: foliated or non-foliated. Non-foliated metamorphic rocks
are classified further by their mineral content while foliated rocks are classified by the grade or severity of
metamorphism that formed them as well as mineral content. There are many examples of each group in
nature, but we will only look at eight today.
Non-foliated Metamorphic Rocks
Quartzite is composed completely of quartz and is entirely crystalline. Look closely as this rock
may have a “fused” appearance, as if grains were melted together.
Marble is composed mostly of calcite and is entirely crystalline. This rock may appear igneous
with large, interlocking crystals, but it is not.
Hornfels is a contact metamorphosed, fine-grained metamorphic rock composed of
predominantly micas (when its parent is shale) or amphiboles (when its parent is basalt). Usually
dark in color, sometimes still has original characteristics of the parent rock evident and can be
confused with foliated texture.
Foliated Rocks
For the purposes of this class, foliated metamorphic rocks are classified based on metamorphic grade, that
is determined by their texture and minerals. Minerals that indicate the highest temperature and pressures
encountered during formation (grade) are called index minerals. The chart below gives some examples of
index minerals and the metamorphic intensity required to produce them.
Index Mineral Commonly linked texture
Metamorphic intensity (grade)
Chlorite mica
Slatey, Phyllitic
Low
Biotite mica
Slatey, Phyllitic
Low to medium
Garnet
Phyllitic, schistose
Medium
Staurolite
Schistose, Gneissic
Medium to high
Talc mica
Gneissic
High
Kyanite
Gneissic
Very high
Amphibole
Severe
Rocks with Slatey Cleavage (i.e., a foliated-slatey or a foliated-phyllitic texture)
Slate is the lowest metamorphic grade rock. It is flat and closely resembles shale except that it is
usually harder than glass and can be slightly more reflective due to larger mica crystals.
Phyllite is only a slightly higher metamorphic grade rock than slate, and has silt-sized crystals of
mica that give it a pronounced shiny or greasy luster.
Rocks with crenulations (these look like wrinkles on the flat surfaces; foliated-phyllitic or foliated
schistose textures)
Phyllite is only a slightly higher metamorphic grade rock than slate, and has silt-sized crystals of
mica that give it a pronounced waxy sheen or greasy luster.
Muscovite schist has very easily seen muscovite flakes among its other crystals, which are
typically sand-sized. This is the lowest grade of schist.
Biotite Schist has very easily seen biotite flakes among its other crystals, which may include
muscovite. This is a medium grade schist.
Garnet Schist has easily seen round red garnet crystals among a matrix of mica crystals like
muscovite and biotite. This is the highest grade of schist.
Rocks with Schistosity - foliated schistose textures
Muscovite schist has very easily seen muscovite flakes among its other crystals, which are
typically sand-sized. This is the lowest grade of schist.
Biotite Schist has very easily seen biotite flakes among its other crystals, which may include
muscovite. This is a medium grade schist.
Garnet Schist has easily seen round red garnet crystals among a matrix of mica crystals like
muscovite and biotite. This is the highest grade of schist.
Other minerals such as staurolite, andalusite and kyanite may also be commonly found in
rocks with a schistose texture.
Rocks with Gneissic Banding (i.e., a foliated-gneissic texture)
Gneiss (pronounced “nice”) is entirely crystalline with alternating bands of light and dark
minerals. The crystals are typically at least the size of coarse sand.
Photo of samples
Texture and Rock name
Slate
Phyllite
Mica Schist
Gneiss
Fall 2016