What is the hardness of a Mineral?
Name: __________________________________
Background:
The hardness of a mineral is its resistance to being scratched. Friedrich Mohs
developed a hardness scale from 1-10. Talc is the softest mineral and therefore is a # 1 on
the scale. Gypsum is twice as hard as talc and therefore was classified as a #2. This pattern
continues 1-9, however diamonds are 40 times harder than talc.
1. Talc 2. Gypsum 3. Calcite 4. Fluorite 5. Apatite 6. Feldspar 7. Quartz 8. Topaz
9. Corundum 10. Diamond
Procedure:
1. Look at the teacher’s example of minerals arranged by hardness. Put your minerals
in the same order. Now you have your own hardness scale.
2. Use Mohs hardness scale to determine the hardness of the following items (put the
highest number that the object CAN scratch):
a. fingernail ____________________
b. copper penny_____________________
c. Steel nail _____________________
d. glass plate_________________________
3. A young lady is greatly surprised when her cheap boyfriend presents her with a
beautiful diamond ring. As he asks her to marry him she cant help but wonder if it is
really a diamond or a cubic zarconia ring. Feigning excitement she excuses herself to
the ladies room to compose herself when in reality she plans to test the “diamond”
against the restroom mirror. The test reveals that the stone does scratch the mirror.
What is your expert opinion about the ring? Do you have any advice for the
prospective bride?
How minerals break
Minerals can be identified by how they break. Some break into geometric shapes identical
to the larger piece from which they were broken from. This is called cleavage. Others
break randomly with no pattern. This is called fracture.
Purpose: In this lab you will identify minerals by how they break.
Minerals needed:
#74 Mica
#13 Sphalerite
#12 Hornblend
#3 Calcite
#108 Serpintine
#6 Feldspar
#4 Fluorite
#34 Halite
#23 Obsidian
Name: __________________________________
Procedure:
You are no longer using the 9 minerals from Mohs hardness scale. Get a set of minerals for
the “cleavage and fracture lab.” Separate your 9 mineral samples into 2 groups; those with
cleavage planes, and those with fracture. List them below. (Hint: only 2 have fracture)
Those with Cleavage
1.
2.
3.
4.
5.
6.
7.
Those with Fracture
1.
2.
Cleavage planes.
Minerals that break with cleavage planes do this because of unequal molecular bonds.
Breaking occurs along these weaker bond causing geometric planes.
Analysis:
1. What are the cleavage angles of your sample of Calcite?
2. Will all samples of Calcite have these same angles?
3. Which 1 of the 9 minerals in your kit broke with conchoidal fracture?
4. Which 1 of the 9 minerals in your kit broke with random fracture?
5. What causes certain minerals to break with cleavage planes?
6. What causes certain minerals to break with fracture?
7. Which of the 9 minerals from the kit would be ideal for making arrowheads and
knives?
Why?
8. Slate has been used for centuries to make flat surfaces (shingles, sidewalk, pool
tables). What mineral from your kit do you think is found in slate?
Why?
10. Which of these 9 minerals is most like your personality and why?