Lab 4
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School
CUNY College of Staten Island *
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Course
101
Subject
Geology
Date
Feb 20, 2024
Type
Pages
9
Uploaded by gzimevukovic
GEO 101
Instructor:
Student:
Mineral
Hardness
Talc
1
Gypsum
2
Calcite
3
Fluorite
4
Apatite
5
Orthoclase
6
Quartz
7
Topaz
8
Corundum
9
Diamond
10
Lab 4 Minerals
In-class lab exercises
Part 1 – Hardness
Hardness
: This is a measure of how resistant a
mineral is to abrasion, and is measured on a scale
called Moh’s scale. The hardest mineral is diamond,
with a hardness of 10, and the softest is talc, with a
hardness of 1. Harness is measured by testing
whether a mineral may be scratched by another
mineral of known hardness (see table on right), or by
another object of known hardness. In the lab you
will be testing minerals with your fingernail
(hardness 2.5), a copper penny (hardness 3.5) and a
glass plate (hardness 5.5). You will therefore be able
to define hardness as < 2.5, 2.5 – 3.5, 3.5 – 5.5 or >
5.5.
Graphite, Hematite, Quartz, and Calcite were tested for hardness using a fingernail, a copper
penny, and a glass plate. The results of the tests are provided below. “Yes” means that the
mineral can be scratched, and “No” means that the mineral cannot be scratched.
Mineral
Fingernail
Penny
Glass Plate
Graphite
Yes
Yes
Yes
Hematite
No
No
Yes
Quartz
No
No
No
1
GEO 101
Instructor:
Student:
Calcite
No
Yes
Yes
Using the hardness test results (table above) and Moh’s hardness scale, list these minerals in
order of their hardness.
Softest
Graphite
Calcite
Hematite
Hardest
Quartz
2
GEO 101
Instructor:
Student:
Part 2 – Cleavage and Fracture
Cleavage and fracture
: There are two different ways that a mineral may break. If it breaks along an
irregular surface, the mineral is described as having fracture. However, if it breaks along a flat surface,
parallel to one of the faces of the crystal, then it is described as having cleavage. Such cleavage planes
are related to the chemical structure of the crystal. The angles between cleavage planes are often
unique to a particular type of mineral, making them a good guide to identification.
Look at the photographs of the following minerals:
Quartz
Halite
Calcite
3
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GEO 101
Instructor:
Student:
Gypsum
Which sample has fracture, but no cleavage planes?
Quartz
All of the other samples have the same number of cleavage planes – how many cleavage planes
do they have?
3
Name the sample where the cleavage planes are at right angles.
Halite
The other 2 samples have very similar cleavage plane angles, but one effervesces when a drop of
acid is placed on its surface (see photographs below). Which sample does this?
Calite
4
GEO 101
Instructor:
Student:
Hint: CaCO
3
+ 2HCl = CaCl
2
(calcium chloride) + H
2
O (water) + CO
2
(carbon dioxide)
5
GEO 101
Instructor:
Student:
Part 3 – Color, streak and luster
Color
: This is the color you see when you look at the mineral. Be specific i.e. say “red, brown and
yellow” rather than “multicolored” or “various”. Also distinguish between white and clear. This may be
different to another sample of the same mineral.
Streak
: This is the color of the mineral when it is powdered. To test for this color, you draw the mineral
across the surface of a piece of white porcelain, called a
streak plate
. The mark the mineral leaves on the
surface shows the color of its streak. This color is much less variable than the general color you see when
looking at the whole mineral. If a mineral is harder than the streak plate, it will not powder. Be careful to
differentiate between a mineral with no streak (because it’s too hard) and one with a white streak
Luster
: This is a property of the mineral’s surface, and is independent from its color. It describes how
the mineral surface reflects light. Two sample of the same mineral may have a different luster.
Metallic – mineral appears shiny like a new coin
Vitreous – mineral looks glassy
Resinous – mineral surface looks like resin or plastic
Pearly – mineral surface looks like a pearl or the inside of a seashell
Dull – mineral reflects little light and looks like dirt or soil
Greasy – mineral surface has a greasy look and feel
Look at the photographs of the following minerals:
Galena
Pyrite
6
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GEO 101
Instructor:
Student:
Hematite
Microcline
What is the 1) color, 2) luster, and 3) streak color of each of these minerals?
7
GEO 101
Instructor:
Student:
Galena
1 Black
2 Greasy
3 Black
Pyrite
1Gold
2Metalic
3Brown
Hematite
1Brown
2Dull
3Red
Microcline
1Salmon
2Dull
Microcline does not leave the streak on a porcelain plate. What does this tell you about the
hardness and the streak of this sample?
It is harder than the plate (the hardness level of the mineral is high) and the streak doesn’t
come up.
Are the color and the streak the same in each mineral? Explain and name 1) a mineral with the
same color and streak and 2) a mineral with different color and streak.
No, they are not the same in each mineral because Galena looks black and its streak is
black, but Hematite is brown but its streak is red.
Take a look at another set of hematite photographs.
8
GEO 101
Instructor:
Student:
Do they all have the same color? Describe the variability.
They do not all have the same color, and they also have different lusters. Some are glassy
and some are on the duller side. The first mineral is brown, the following two are black,
and the last one is red.
What is the one thing that is consistent among all of the hematite samples?
The streak color is the same for all the samples.
9
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