Transcript What is the hardness of Mineral A?

Mr. Harper’s science mini lesson
with audio
Mineral
Hardness
The mineral
“scratch” property
Rocks are made of a mixture
of ingredients
called minerals.
When we identify minerals, we use
samples of the pure minerals. These
are different from rocks. Rocks are a
mixture of minerals, but the samples
we use are made of just one mineral.
In fourth grade we do some tests with
mineral samples to discover their
properties, then find the name of the
mineral of the Mineral Identification Chart.
This Powerpoint program deals only with
the mineral property of hardness.
You can watch the “Mineral Properties”
Powerpoint to learn about other mineral
properties
(color, luster,
streak, cleavage).
Hardness is the property of how
difficult it is to scratch a mineral.
Some minerals are so soft you can
scratch them with a fingernail.
Some minerals are so hard
that they can scratch glass.
The Moh’s Hardness
Scale is what geologists
use to rate the hardness
of minerals on a scale
from 1 to 10.
There are a lot more than
10 minerals that make up all
the rocks in the world,
but the ten minerals on the
Moh’s Hardness Scale
happen to have the hardness
of the number they represent.
softer
Talc is the softest
mineral, so it gets the lowest
//
number. Talc is number 1 on the Moh’s Hardness
Scale. Every other mineral can scratch talc. Even
a fingernail can easily scratch talc.
Talc is also called soapstone
because it feels soft like soap.
Talc is so soft that it is used in baby powder.
The hardest mineral on Earth is diamond.
It has the highest number on the Moh’s
Hardness Scale; 10. This means that a
diamond can scratch any mineral, except
another diamond.
harder
Remember:
harder scratches softer
Higher Moh’s number are Harder
Smaller Moh’s numbers are softer
Higher Moh’s numbers can
scratch smaller Moh’s numbers.
Any mineral can scratch every mineral that
is softer (has a smaller Moh’s number).
The harder mineral will always scratch the softer mineral.
5.5
2
6
3
A mineral cannot scratch any mineral that
is the same hardness or harder
(equal or greater Moh’s number).
Sometimes the
Moh’s Scale is
shown with
10 (diamond) at
the top and 1 (talc)
at the bottom. But
bigger numbers are
always harder than
smaller number.
Just remember:
Higher is Harder
and
Smaller is Softer
on the Moh’s Hardness Scale
Human fingernails all have a hardness
of about 2.5, (between 2 and 3).
So if your fingernail can scratch a
mineral, that mineral has a hardness of 1 or 2.
We can be sure that a mineral’s hardness is less
than 2.5 if a fingernail can scratch it.
A fingernail cannot scratch another
fingernail because they are the same
hardness.
Minerals or any other object cannot
scratch or be scratched by an object of
equal hardness.
A mineral or any object that can scratch your
fingernail must have a hardness of at least 3.
And of course, any mineral with hardness greater
than 3 can scratch your fingernail.
Two pieces of the same kind of mineral
cannot scratch each other because they
are the same hardness. An object can
only be scratched by a harder object.
A copper coin has a
hardness of 3.5.
This means a penny
can scratch any
mineral with a
hardness number
of 1, 2, or 3.
A penny cannot
scratch a mineral
with hardness of
4, 5, 6, 7, 8, 9 or 10.
Quartz has a Moh’s
hardness of 7.
A piece of quartz
can scratch any
mineral with a
hardness of 6 or
lower. Quartz
cannot scratch
a 7 or higher.
A diamond has
Moh’s hardness
of 10.
A diamond can
scratch any
mineral except
another diamond.
A note here:
Hardness is different from strength.
A baseball is strong
enough to break glass
but is not hard enough
to scratch glass.
Glass isn’t strong
enough to break a
baseball, but it’s
hard enough to
scratch a baseball.
Note:
Breaking or crumbling is not the same as scratching.
If you scratch a mineral there will be a thin line that
won’t rub off. If the mark rubs away then it was only
a pencil-like mark from the object you were using to
make the scratch.
Remember:
harder scratches softer
Higher Moh’s number are Harder
Smaller Moh’s numbers are softer
Higher Moh’s numbers can
scratch smaller Moh’s numbers.
Now, let’s see how
well you understand
mineral hardness.
Test
1
Mineral
We want to find the hardness of a mineral
sample labeled “Mineral A.”
We try to scratch Mineral A with a piece of
calcite that we know has a hardness of 3.
Mineral A can scratch the calcite, but the
calcite cannot scratch Mineral A.
What is the hardness
of Mineral A?
A
Test
Mineral
1 A>3
A
All we know for sure is that
Mineral A is harder than 3
(because it could scratch a 3).
We need more information to find the exact hardness
of Mineral A.
Test 1
A>3
Test
2
Mineral
A
We take a piece of feldspar (hardness 6)
and try to scratch Mineral A.
Mineral A cannot scratch feldspar but
feldspar can scratch Mineral A.
What is the hardness
of Mineral A?
Test 1
A>3
Test 2
Mineral
A
A<6
If feldspar (6) can scratch it, then the
hardness of Mineral A must be less than 6.
We now know that Mineral A is 3-6
(harder than 3 but softer than 6).
Test 1
Test 2
Test
3
A>3
Mineral
A
A<6
We do the scratch test on Mineral A with a
sample of fluorite that we know has a
hardness of 4. Fluorite cannot scratch
Mineral A, and Mineral A cannot scratch
the fluorite.
What is the hardness of Mineral A?
Test 1
Test 2
Test 3
A>3
A<6
Mineral
A
A=4
Any two minerals that cannot scratch each other
have the same hardness.
If we know fluorite is hardness 4, then Mineral A
must also be hardness 4.
This also makes sense with our other tests that
showed a hardness between 3 and 6.
Use the Moh’s Hardness Scale to help you with Mineral B
Test
1
We try to scratch a sample of
mineral B with a fingernail.
Mineral B cannot be scratched
by our fingernail.
What do we know
about the hardness
of Mineral B?
Mineral
B
Use the Moh’s Hardness Scale to help you with mineral B
Test 1
B > 2.5
The Moh’s Hardness Scale
shows that a fingernail has
a hardness of 2.5.
If a fingernail cannot scratch
it, then the hardness of
Mineral B must be greater
than 2.5
Mineral
B
Mineral
Test 1
B > 2.5
Test
2
We try to scratch Mineral B
with a copper penny.
Mineral B is scratched
by the penny.
What do we know
about the hardness
of Mineral B?
B
Mineral
Test 1
B > 2.5
Test 2
B < 3.5
The Moh’s Scale shows that a
copper penny has a hardness of
3.5, so if a penny can scratch it
Mineral B must be softer than
3.5 hardness. So, if it’s greater
than 2.5 and less than 3.5,
we just figured out that the
hardness of Mineral B = 3
B
Use the Moh’s Hardness Scale to help you.
Can calcite
scratch
gypsum?
Use the Moh’s Hardness Scale to help you.
Yes calcite (3)
can scratch
gypsum (2).
Higher numbers are harder
and can scratch any
smaller number which is softer.
Use the Moh’s Hardness Scale to help you.
Can quartz
scratch
diamond?
Use the Moh’s Hardness Scale to help you.
No, quartz (7)
cannot scratch
diamond (10).
Smaller numbers are softer
and cannot scratch
higher numbers which are harder.
You can find out more about mineral
hardness on Brainpop
• Mineral Identification