Download igneous rock lab _13

LAB #14
Name ____________________________________ Lab Period _______
Igneous Rock Identification
Problem
What are the characteristics of igneous rocks?
Materials
Eight igneous rocks: granite, basalt, rhyolite, gabbro, pumice, diorite, scoria and obsidian.
Magnifying glass
Vertical Scale (instructions on how to make this are in Part III of the lab)
ESRT
Procedure
PART I
1. For each sample, determine:
o
Color: light, dark or mixed. List the sample # and its color in the Data Table
o
Texture: The crystals can be large and visible, small and difficult to see or not visible
at all
2. Intrusive or Extrusive- Intrusive rocks have large crystals (cooled longer below the surface),
extrusive rocks have small or no crystals (cooled quickly on the surface).
3. Use the flow chart on the second page to determine the rock’s identity.
4. Use the Igneous Rock Chart in the Earth Science Reference Tables (p.6) to determine the
minerals present in each sample.
Data Table
Sample
Color
Texture
Intrusive or
Extrusive
Rock Name
Minerals
Present
1
2
3
4
5
6
7
8
1
Identification Flow Chart
Light Colored
Granite
Light & Dark
Diorite
Dark Colored
Gabbro
Light Colored
Rhyolite
Dark Colored
Basalt
Coarse
Texture
Fine
Light
Pumice
Dark
Scoria
No Crystals with holes
No crystals (glassy)
Obsidian
PART II
5. Use the ESRT p. 6 to name the following igneous rocks:
Description
a. Intrusive, felsic composition, coarse
b. Extrusive, glassy, high density, non-vesicular
c. Volcanic, fine grained, high density, non-vesicular
d. Coarse grained, mafic composition, mostly olivine and
pyroxene
e. Low density, glassy, may appear black
f. Light color, grain size less than 1mm, non-vesicular
g. Plutonic, 40% quartz, very coarse
h. Dark color, 50% pyroxene, grain size 1 mm
i. Noncrystalline, Al composition, usually density <1
Rock Name
PART III
6. Make a vertical scale using the directions below.
o Use a thin strip of any blank paper about 6 inches long and 1 inch wide
 GO TO ESRT page 6
 SEE Scheme for Igneous Rock Identification
 GO TO ‘Mineral Composition’ and copy the scale
 It’s on the left hand side
 Copy it EXACTLY onto your strip of paper
7. THEN…ESTIMATE the percent (%) of each mineral in these ROCKS
o HOW can I do this? – HERE’s HOW…
o Find the rock that you want in the IGNEOUS ROCKS list (on the chart at the
bottom of lab page 6- it looks like ESRT p.6)
2
o Make a LIGHT pencil line straight down from the MIDDLE of the rock type through
to the mineral composition chart
o Estimate % of each mineral in the rock type USING
 The scale you just made
 Line it up with the light pencil line you just drew
 Put the 0% on the bottom edge of the range for each mineral (on the chart
at the bottom of page 6).
 READ off the % at the top edge of the mineral (on the chart at the bottom
of page 6).
o Write the % of each mineral on the igneous ID chart below, if there is none of that
mineral just write 0%.
Mineral Percentage Chart
Rock you
Mineral
Composition
*All minerals are NOT in all rocks
Want
Andesite
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____%
3
Granite
K Feldspar_____%
Amphibole_____%
Quartz ____%
Pyroxene______%
Plagioclase_____%
Olivine______%
Biotite____%
Questions and Conclusions
1. An igneous rock is a rock that forms from
2. Define:
o Magmao Lava-
3. Describe the size of the crystals you would expect to see in:

Intrusive rocks-

Extrusive rocks-
5. What two factors determine the crystal size in an igneous rock?
6. How can two different rocks have the same mineral composition? (Hint: Think of two
characteristics that are used to classify igneous rocks.)
4
Practice Regents Questions
1. Variations of mineral composition can be
observed in the Palisades Sill in southeastern
New York State. The Palisades Sill is an
intrusive igneous rock called diabase. It is
composed mainly of 50% pyroxene, 40%
plagioclase and 5% olivine.
Which other igneous rock is closest to diabase in
mineral composition?
1. andesite
2. granite
1. age, density, and smoothness
2. cleavage, color, and abundance
3. hardness, cleavage, and crystal shape
4. chemical composition, size, and origin
3. Identify 3 minerals that can be found with
quartz in andesite rock.
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.
1. gabbro
2. marble
3. breccia
4. pumice
3. rhyolite
4. gabbro
2. Different arrangements of tetrahedral in the
silicate group of minerals result in differences in
the minerals'
1.
2.
3.
4.
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:
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. high concentration of aluminum and a low
concentration of silica
4. low concentration of aluminum and a low
concentration of silicon
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,
gneiss** and hornfels**?
1.
2.
3.
4.
quartz
calcite
pyroxene
olivine
5. Which common rock is formed from the
solidification of molten material?
1. rock gypsum
3. rhyolite
2. slate
4. coal
quartz
pyroxene
olivine
muscovite mica
** see ESRT pg7 Metamorphic Rock ID
(composition)
10. Which mineral, found in granite, will scratch glass
(hardness = 5.5), but not pyrite?
(1) gypsum
(2) fluorite
(3) orthoclase
(4) quartz
5
6