Lab 3
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New Mexico State University *
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1110G
Subject
Geology
Date
Dec 6, 2023
Type
docx
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Uploaded by DoctorCheetahPerson1995
GEOL 111
Lab 3 Worksheet
Igneous Rocks
1.
Igneous Rock Textures
a.
On the Igneous Rock Identification main page use the ID chart and
provided links to identify the texture of each sample. Texture is
defined as the size, shape, and arrangement of the grains or crystal
in each rock. These terms include: pegmatitic (very coarse-grained),
phaneritic (coarse-grained), aphanitic (fine-grained), glassy,
porphyritic (large grains in a fine background, vesicular (holes)
Sample
Texture
1.
Aphanitic
3.
Phaneritic
5.
Phaneritic
7.
Glassy
9.
Porphyritic
11.
Porphyritic
b.
For this section you’ll be interpreting the texture as to the cooling
rate and cooling environment. Igneous crystals form when the atoms
in melted rock become arranged in orderly patterns while they cool.
It takes a long time for orderly arrangements to grow large enough to
be seen. If melted rock cools in a short time, the crystals remain
small. If melted rock cools instantly, no patterns are formed and the
rock texture will be glassy. In a volcano if magma starts cooling
slowly, large crystals will form, but if it erupts, the remaining liquid
forms small crystals around the large crystals. If magma doesn’t cool
until it reaches the surface, then small crystals will form. For each of
the samples shown identify:
the cooling rate: fast, slow, or two-staged and
cooling environment: magma chamber, eruption from volcano, or
deep cooling followed by eruption.
Sample
Cooling
Rate
Cooling Environment
2.
Two-Staged
Deep Cooling followed
by eruption
4.
Slow
Magma Chamber
GEOL 111
Lab 3 Worksheet
Igneous Rocks
Sample
Cooling
Rate
Cooling Environment
6.
Fast
Magma Chamber
8.
Fast
eruption from volcano
10.
Fast
eruption from volcano
12.
Fast
eruption from volcano
2.
Igneous Rock Sample Identification
. From the Samples to Identify listing
find (sample number and name)
Description
Sample Name and Number
A fine-grained mafic extrusive
rock, its crystals are only visible
with a magnifying lens. There are
holes in the rock, called vesicles,
which show where gas bubbles
were trapped as the melted rock
solidified.
Scoria, 10
This rock has a porphyritic, or
mixed texture and is an
intermediate composition igneous
rock
Andesite, 11
This rock is a felsic pyroclastic
igneous rock
Pumice, 8
This rock has a glassy texture. It
has shiny curved surfaces and
sharp edges. Even in a magnified
view, this rock shows no crystals.
Obsidian, 7
This felsic rock has a phaneritic
texture
Granite, 5
This is an ultramafic igneous rock
Dunite, 3
Be sure to take advantage of the radio buttons in the chart below each
sample. It'll let you know if you are correct.
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