PowerPoint Presentation

Mr. Harpers science mini lesson with audio

Mineral HardnessThe mineral scratch property

1// 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 hard that they can scratch glass.

Some minerals are so soft you can scratch them with a fingernail.

6

The Mohs 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 Mohs Hardness Scale happen to have the hardness of the number they represent. //

Talc is the softest mineral, so it gets the lowest number. Talc is number 1 on the Mohs Hardness Scale. Every other mineral can scratch talc. Even a fingernail can easily scratch talc.softer

Talc is so soft that it is used in baby powder.

Talc is also called soapstone because it feels soft like soap.

9////

The hardest mineral on Earth is diamond. It has the highest number on the Mohs Hardness Scale; 10. This means that a diamond can scratch any mineral, except another diamond.harder

//Remember: harder scratches softer

Higher Mohs number are Harder

Smaller Mohs numbers are softer

Higher Mohs numbers can scratch smaller Mohs numbers.

Any mineral can scratch every mineral that is softer (has a smaller Mohs number).

A mineral cannot scratch any mineral that is the same hardness or harder (equal or greater Mohs number).

65.523The harder mineral will always scratch the softer mineral.

// Sometimes the Mohs 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 andSmaller is Softer on the Mohs Hardness Scale

Human fingernails all have a hardness of about 2.5, (between 2 and 3).So if your fingernail can scratch amineral, that mineral has a hardness of 1 or 2. We can be sure that a minerals 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 Mohs 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 Mohs hardness of 10. A diamond can scratch any mineral except another diamond.

A note here:Hardness is different from strength.

Glass isnt strong enough to break a baseball, but its hard enough to scratch a baseball.A baseball is strong enough to break glass but is not hard enough to scratch glass.

// Note:Breaking or crumbling is not the same as scratching. If you scratch a mineral there will be a thin line that wont 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 Mohs number are Harder

Smaller Mohs numbers are softer

Higher Mohs numbers can scratch smaller Mohs numbers.

//Now, lets see how well you understand mineral hardness.

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.1What is the hardness of Mineral A?TestMineral 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.1TestMineral A

A > 3All we know for sure is that Mineral A is harder than 3. We need more information to find the exact hardness of Mineral A.2We 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?TestTest 1Mineral A

A > 3If 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).What is the hardness of mineral A?Test 1Test 2Mineral A

A > 3A < 6Test

What is the hardness of Mineral A?Test 1Test 2We 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.3Mineral A

A > 3A < 6Test

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.Test 1Test 2Test 3Mineral A

A > 3A = 4A < 6We try to scratch a sample of mineral B with a fingernail. Mineral B cannot be scratched by our fingernail.Use the Mohs Hardness Scale to help you with Mineral BMineral B

1TestWhat do we know about the hardness of Mineral B?

Use the Mohs Hardness Scale to help you with mineral BMineral B

The Mohs 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 2.5Test 1B > 2.5

Mineral B

Test 12TestWe 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 > 2.5Mineral B

Test 12TestWhat do we know about the hardness of mineral B?Test 2The Mohs 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 its greater than 2.5 and less than 3.5, we just figured out that the hardness of Mineral B = 3B > 2.5B < 3.5

34Use the Mohs Hardness Scale to help you.

Can calcite scratch gypsum?

Use the Mohs 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 Mohs Hardness Scale to help you.

Can quartz scratch diamond?

Use the Mohs Hardness Scale to help you.

No, quartz (7) cannot scratch diamond (10).Smaller numbers are softer and cannot scratchhigher numbers which are harder.

Mineral IdentificationYou can find out more about mineral hardness on Brainpop