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Talc is a metamorphic mineral. It is the softest of the minerals in the scale. You can scratch talc with your fingernail. Talcum powder is made from ground up talc. Of course, the nice smell is put in after he talc is ground up.

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Gypsum is a sedimentary mineral. It is harder than talc, but you can still scratch it with your fingernail. Gypsum may be colorless or white. It is found in huge beds in the ground where it is dug out. Gypsum is an important mineral. Plaster of Paris is made from it. Plaster wallboard is also made from gypsum. Did you know that the old blackboard chalk you used in school was made from gypsum?

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Calcite is third in the hardness scale. It scratches talc and gypsum. You can scratch calcite with a penny. Calcite is a colorless or white mineral. You will find it in many places and with all groups of rocks. A special form of calcite is Iceland spar. When you look through a clear crystal of Iceland spar, everything suddenly looks double!

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This mineral is one of the most colorful of the hardness minerals. Crystals of fluorite may be white, gray, black and many other colors. They may also be colorless. Fluorite is four on the hardness scale, but you can scratch it with a small pocket knife.

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Apatite is another mineral that forms beautiful crystals of many different colors. Some of these colors are white, brown, green, violet, blue and yellow. Yellow is the most common color. You can scratch apatite with a knife, too. Apatite in turn will scratch any of the hardness minerals below it. Apatite, like each of the other minerals, is able to scratch itself.

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Feldspar is about the most common mineral on the earth. When this mineral breaks up and rots, it turns into clay. Clay is found almost everywhere. Your knife will not scratch feldspar, but the feldspar will scratch your knife!

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Quartz is a common mineral you have already read about. It comes in many colors. A beautiful kind of quartz is names Tiger’s Eye and is used in jewelry. Quartz sand is melted and turned into clear glass. Radios and phonographs very often have special quartz crystals in them. Quartz is very useful. It is the hardest mineral you are apt to find easily.

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Topaz is a very hard stone. It will scratch quartz or any of the other minerals below quartz. Topaz is prized as a gem stone because it is very beautiful. This stone is commonly yellow.

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Corundum also known as Ruby, is next to the hardest minerals. Some crystals of this mineral are also gem stones. Ruby is a clear red corundum crystal. Such a crystal is quite valuable. Ordinary corundum is crushed into small bits and made into sandpaper.

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This is the hardest mineral known on earth. Nothing is harder than diamond. It is many times as harder as corundum. Clear crystals are made into jewels. Dark-colored diamonds are used to polish and cut other hard stones, as well as other diamonds, too. Diamonds are valuable because they are very hard, beautiful and rare.

These are the hardest minerals. They are all used for many things. Testing the hardness of other minerals is just one of the things for which they are used. As you become more interested in rocks and minerals, you will want to have a set of hardness testing minerals. A set is not expensive, for most sets do not contain a diamond. Since a diamond could only test another diamond, there is little need for one in the set. Many of the tests can be made with the fingernail, a penny, a pocket knife and a piece of quartz.