CLASS SET
What is a Mineral?
A mineral is a homogeneous inorganic substance which has a more or less specific chemical composition and fairly
definite physical properties. In a restricted sense, substances resulting from the processes of plant and animal life, such as
coal, petroleum, animal bones, and pearls are not classed as minerals. Most minerals are characterized by crystal faces,
the flat smooth surfaces of a crystal. Of particular importance are the physical properties of minerals because familiarity
with them facilitates a rapid identification of the mineral specimen that may be collected almost anywhere.
PHYSICAL PROPERTIES USED IN THE IDENTIFICATION OF MINERALS
1. Hardness
Hardness is expressed as the resistance that a smooth surface of a given mineral offers to scratching. See
Figure 1: The horizontal axis of the graph is divided into 10 equal units based on Moh’s scale of hardness. The
vertical axis, which is based on absolute units, emphasizes how the interval of hardness between different pairs of
in the scale varies. The scale means that any mineral can scratch the mineral listed below it. It is advisable to try
to scratch mineral A with mineral B, and then reverse the procedure. A fresh surface must be used for this test
because mineral B may leave a mark on mineral A which appears to be permanent. However, the mark may only
be a powered streak of the softer mineral which can be rubbed off.
Figure 1
Tools that are commonly used in field to measure the hardness of a mineral specimen are:
 Fingernail
2.5
 Copper Coin
3.5
 Iron Nail
5.5
 Glass Plate
6.0
2. Streak
The streak of a mineral is the color obtained by finely powdering the mineral.
Powdering is usually achieved by rubbing a piece of the mineral on an unglazed porcelain plate known as a streak
plate.
3. Color
The attractive colors which minerals display constitute one of the quickest aids to identification. Some
caution must be exercised, however, for the following reasons:
 Certain minerals occur in a wide variety of colors
 Impurities often give a mineral a false color which is not characteristic of it.
 A change in color is often produced by a change in composition
 Exposure to the atmosphere may alter the surface of a mineral, tarnishing it or changing its color. In this case
the mineral should be broken thus exposing a fresh surface which shows the true color.
4. Luster
The way a mineral reflects light is known as luster. The luster of minerals is divided into two major types
– Metallic and non-metallic. Metallic minerals, such as galena usually have a dark appearance and a dark streak
in contrast to non-metallic minerals. The luster of non-metallic minerals is further subdivided into several types.
For example quartz has a glassy or vitreous luster while talc has a pearly luster.
5. Cleavage
Some minerals exhibit the property of breaking along smooth, flat surfaces, which are called cleavage
planes. The number and direction of cleavage planes are diagnostic physical properties for a given mineral.
Minerals that do not have good cleavage exhibit rough and irregular broken surfaces known as fracture surfaces.
Biotite mica is an excellent example of cleavage in one direction. The thin sheets of the mineral can literally be
peeled apart. Calcite has perfect cleavage in three directions which results in rhomboid shaped fragments. No
matter how small the pieces are, they always exhibit the same form depending upon the type of cleavage.
6. Specific Gravity
Specific gravity is an expression of the weight of a mineral compared with the weight of an equal volume
of water. Thus, galena, which has a high specific gravity, feels “heavy”, whereas halite, with a relatively low
specific gravity feels “light”. In some mineral identification tables the specific gravity is simply categorized as
high, medium, or low. In general, ore minerals have high specific gravities and rock-forming minerals have low
specific gravity.
7. Magnetism
Some minerals, such as magnetite, are magnetic and can be easily tested with a magnet.
8. Taste
Although this test is not recommended for every mineral, it is used to easily identify the salty mineral
halite.
9. Double Refraction
Some varieties of the mineral calcite can split light into two rays creating a double image.
10. Acid Test
The acid test is used to identify the mineral calcite, which contains calcium carbonate (CaCO3). When
dilute hydrochloric acid is dropped onto calcite a reaction occurs and the mineral effervesces or fizzes.
Carbon dioxide (CO2) gas is being released from the (CO3) calcium carbonate.
11. Double Refraction
Some varieties of the mineral calcite can split light into two rays creating a double image.
12. Acid Test
The acid test is used to identify the mineral calcite, which contains calcium carbonate (CaCO3). When
dilute hydrochloric acid is dropped onto calcite a reaction occurs and the mineral effervesces or fizzes.
Carbon dioxide (CO2) gas is being released from the (CO3) calcium carbonate.
Types of Cleavage in One to Four Directions
Conchoidal Fracture – (literally, shell-like) - A type of fracture that produces a smooth, curved surface.
It is characteristic of quartz, obsidian, glass and flint.
READ THIS STORY TO ANSWER QUESTIONS 20-24 IN YOUR PACKET
It is 7:00am and you are awakened by calls to get up and get ready to go to school. You hop out of
bed and head for the bathroom. After a quick shower with your favorite scented anti bacterial
body wash you brush your teeth with the latest whitening toothpaste and blow your hair dry.
Back in your room you quickly dress and then rush to the kitchen for a bowl of Iron Man muscle
building fortified cereal, a bacon and egg sandwich with salt and pepper, and a glass of juice. As
you are eating you glance at the battery powered clock hanging on the newly painted kitchen wall,
and realize that you are right on schedule for the bus. Before heading out the door you check your
book bag to make sure that you have pens, pencils and paper. Wrapping a rubber band around
some flash cards you toss them into the bag, and head out the door. In order to be at the bus stop
a little early, you hurry out the door and down the concrete sidewalk to the corner.
As you approach the corner, you slow your stride to a casual, but oh, so cool, walk and give her
that gleaming white, you can’t resist me smile. She looks great this morning, with just the right
touches of make-up. The dramatic eye shadow and lipstick look just “killer”. You also notice that
this morning she is wearing the cool grey crystal and gold colored metallic bead earrings that you
gave her for her birthday last week. You know in your heart that, at least in part, because of the
minerals in your life it is going to be a really great day.
She smiles back and compliments you on your cool new iPod…
In less than the time it took to board the school bus, you have encountered or utilized dozens of
minerals. Do you how and when? Can you identify them? Don’t you think the minerals in your
life deserve more respect? After all, she does look really cool wearing those earrings! Realizing all
that minerals do for you, you make a commitment. Today is the day to begin to know your
minerals better.
What is a Mineral?
Guided Reading Worksheet
Name ________________________________________
Date __________________________ Period _________
1. Define a mineral using the five characteristics common
to all minerals. (I
SODA)
A Mineral Is…
I
S
O
2. What are five physical properties that can be used to identify
and unknown mineral?
D
A
Physical Properties Used to Identify an Unknown Mineral
1
2
3
4
5
3. How is streak different from color?
4. What is hardness?
5. What four tools can be used to test for hardness?
6. What is the hardness of talc _______, quartz ________, diamond ________, Gypsum ________?
7. Why is color not a reliable property for mineral identification?
8. Moh’s hardness scale indicates that a minerals can scratch another (above or below) it?
9. Which is harder, a copper penny or calcite?
10. What are the two main types of luster?
11. What type of luster does talc have?
12. How is cleavage different from fracture?
13. What mineral has cleavage in one direction?
14. What mineral has conchoidal fracture?
15. The ratio of the weight of a mineral specimen to an equal volume of water is called what?
16. What “types” of minerals have a high specific gravity?
17. What “types”of minerals have low specific gravity?
18. Which mineral is easily identified by its taste?
19. Which test can be quickly used to identify calcite?
Product
Toothpaste
Pencil
Concrete
Jewelry
Glass
salt
cosmetics
drywall
Rubber
Mineral
Answer the following questions after reading the story on the class set.
20. If something is not made from a plant or an animal what is it made from?
21. Are rocks and minerals the same thing? How are they similar? Different?
22. What characteristics would you use to describe or define minerals in general?
23. What physical properties would you use to identify a specific mineral?
24. What are some other products or materials you use that have a mineral or combination of minerals as ingredients?