Topic – How Hard Is That?

How Hard Is That?

Our world is full of rocks. They are everywhere. Rocks can be as big as a mountain or as small as a grain of sand.

There are many types of rocks. All rocks are made up of two or more minerals. There are about 4000 minerals on Earth. Different minerals can combine to make different rocks. That is one of the reasons there are so many types of rocks.

Each mineral is made up of one substance. If you cut a mineral into pieces, each piece would look the same throughout. If you cut a rock into pieces, each piece would look different. Some minerals that you might know are gold, copper, and quartz.

Properties of Minerals

It is not always easy to tell the difference between minerals. People who study minerals use properties or characteristics to identify them. Some properties they use are

•  colour     •  lustre, or how shiny they look in light     • hardness

•  transparency, or how much light shines through them

Here, we will talk about mineral hardness.

Hardness

Some minerals are very hard; others are very soft. The Mohs Hardness Scale is used to compare the hardness of any mineral. The scale lists 10 common minerals from softest (1) to hardest (10). Each mineral can only scratch the minerals that have a lower number than it on the scale.

You can use the minerals on the scale to test other minerals for hardness. For example, talc is the softest (number 1). If you used talc to scratch another mineral and it left a mark, then the mineral is softer than talc. If it did not leave a mark, then it is harder than talc. Diamond is the hardest (number 10). Diamonds will scratch almost any other mineral.

You can also test the hardness of minerals using other things. The chart below tells how to test to find out where a mineral fits on the scale from 1 to 6 using everyday tools.

Scale	Description
1	can be scratched easily with your fingernail; crumbles
2	can be scratched with your fingernail
3	can be scratched with a copper penny
4	can be scratched easily with a nail or a pocket knife
5	can be scratched with a nail or a pocket knife
6	can be scratched with a steel file

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