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.
// 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.
Remember:
harder scratches softer
H
igher Moh’s number are
H
arder
S
maller Moh’s numbers are
s
ofter
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:
H
igher is and
H
arder
S
maller is
S
ofter 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
H
igher Moh’s number are
H
arder
S
maller Moh’s numbers are
s
ofter
Higher Moh’s numbers can scratch smaller Moh’s numbers.
Now, let’s see how well you understand mineral hardness.
Test 1 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?
Mineral A
Test 1
A > 3
Mineral 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
Mineral A
Test 2 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
A < 6
Mineral A
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 A > 3
Mineral A
Test 2 A < 6 Test
3
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
A > 3
Test 2
A < 6
Mineral A
Test 3
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.
Mineral B What do we know about the hardness of Mineral B?
Test 1 Use the Moh’s Hardness Scale to help you with mineral B
B > 2.5
Mineral B 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
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?
Mineral B
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, i f it’s greater than 2.5 and less than 3.5, we just figured out that the hardness of Mineral B = 3 Mineral 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
•