Geology Lab % Minerals in Igneous Rock
Name: _______________________________________________ Date: __________________________
Materials Earth Science Reference Table - Scheme for Igneous Rock Identification
Pencil(s)
A vertical scale – use a thin strip of blank paper about 12 cm long and 2.5 cm wide.
Refer to ESRT page 6, graph at bottom of the page, see Scheme for Igneous Rock Identification and
go to ‘Mineral Composition’ and copy the scale on the left hand side onto your strip of paper
Matching – Match word in Column A with most correct description from Column B - Write the correct
letter from Column B in the Answer Column
Answer
Column
Column A
Column B
1
Mafic
A. Crystals < 1 mm in size
2
Glassy texture
B. Crystals = 1 to 10 mm in size
3
Very coarse texture
C. rocks with gas pockets
4
Intrusive rocks
D. high density & usually dark rock
5
Fine texture
E. Very Mafic with coarse texture
6
Felsic
F. lower density & usually light rock
7
Extrusive rocks
G. large crystal size
8
Coarse texture
H. Crystals > 10 mm in size
9
Vesicular
I.
10
Dunite
J. small crystals or no visible crystals
no visible crystals
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Name a rock made only of QUARTZ______________________________.
Name a rock made only of OLIVINE_______________________________.
TO ESTIMATE the percent (%) of each mineral in these rocks
1. Find the rock that you want in the IGNEOUS ROCKS list (on the chart at the bottom of page 6)
2. Make a LIGHT pencil line straight down from the MIDDLE of the rock type through to the
mineral composition chart
3. Estimate % of each mineral in the rock type using the vertical scale you just made.
4. Line it up with the light pencil line you just drew.
5. Put the 0% on the bottom edge of the range for each mineral (on the chart at the bottom of
page 6)
6. READ off the % at the top edge of the mineral (on the chart at the bottom of page 6)
7. Write the % of each mineral on the igneous ID chart
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USE ESRT (page 6/16) – Scheme for Igneous Rock Identification chart
Rock
Extrusive or
Intrusive
Grain Size
Andesite
Texture
Mineral Composition
K Feldspar_____%
Amphibole_____%
Quartz ____%
Pyroxene______%
Plagioclase_____%
Olivine______%
Biotite____%
Gabbro
K Feldspar_____%
Amphibole_____%
Quartz ____%
Pyroxene______%
Plagioclase_____%
Olivine______%
Biotite____%
Peridotite
K Feldspar_____%
Amphibole_____%
Quartz ____%
Pyroxene______%
Plagioclase_____%
Olivine______%
Biotite____%
Obsidian
K Feldspar_____%
Amphibole_____%
Quartz ____%
Pyroxene______%
Plagioclase_____%
Olivine______%
Biotite____%
Granite
K Feldspar_____%
Amphibole_____%
Quartz ____%
Pyroxene______%
Plagioclase_____%
Olivine______%
Biotite____%
Note: *All minerals are NOT in all rocks…
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Circle the correct answers:
1. Variations of mineral composition can be
observed in an intrusive igneous rock called
diabase. It is composed mainly of 50% pyroxene,
40% plagioclase and 5% olivine
6. Some Moon rock samples have coarse intergrown
crystals composed of plagioclase feldspar, hornblende,
and olivine. These Moon rock samples are most similar
to Earth rock samples of
Which other igneous rock is closest to diabase in
mineral composition?
1. gabbro
3. breccia
1. andesite
3. rhyolite
2. marble
4. pumice
2. granite
4. gabbro
2. Different arrangements of tetrahedral in the
silicate group of minerals result in differences in the
minerals'
1. age, density, and smoothness
2. cleavage, color, and abundance
7. Which relative concentration of elements is found in a
felsic rock?
1. high concentration of silicon and a low
concentration of iron
2. high concentration of iron and a low
concentration of aluminum
3. hardness, cleavage, and crystal shape
4. chemical composition, size, and origin
3. high concentration of aluminum and a low
concentration of iron
4. high concentration of aluminum and a low
concentration of silicon
3. Identify 3 minerals that can be found with quartz
in andesite rock.
1.
2.
3.
4.
potassium feldspar, olivine and biotite
amphibole, olivine and biotite
plagioclase amphibole and olivine
plagioclase, amphibole and biotite
4. For an igneous rock to be classified as rhyolite, it
must be light colored, be fine grained and contain
1.
2.
3.
4.
8. In identifying igneous rocks the feature of texture is
best described as
1.
2.
3.
4.
the way a rock feels
the size of mineral crystals
the color and clarity
number of holes per square cm
9. Which mineral can be found in granite, andesite?
1.
2.
3.
4.
quartz
calcite
pyroxene
olivine
quartz
pyroxene
olivine
biotite mica
5. Which common rock is formed from the
solidification of molten material?
10. Which mineral will scratch glass (hardness = 5.5),
but not pyrite?
1. rock gypsum
2. slate
(1) gypsum
(2) fluorite
3. rhyolite
4. coal
(3) orthoclase
(4) quartz
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