WHAT ROCKS ARE MADE OF.
We have learned that soil is made from rock. Now we ought to learn something about rocks them selves. Rocks are very useful in many ways. It is in the rocks that we find gold and other minerals.
We have seen rocks in many places. In the hills and mountains they are sticking out of the ground. Along the ocean shore and in the canons the waters have washed the soil away and left them bare.
Do you know what a quarry is? It is a place where rock is obtained for buildings. The rock which we find on the top of the ground is dirty and often crumbles easily. It is changing to soil. To get clean, hard rock men open a quarry.
To do this they first scrape away the soil. Then they use powder and blast the rock out until they get down where it is fresh. Then care is used, in breaking the rock, to get pieces of the right size. After the rock is broken hammers and chisels are used by the men, to shape the pieces as they wish.
Many kinds of rock are used for buildings. Granite will be the most interesting to us, and so we will study a chip of that rock.
Here is a piece of granite just from the quarry. I am sure that we have all seen granite. The piece is speckled with little grains of different color. Let us see what these grains are.
Here is one that is clear and looks like a piece of glass. It is so hard that you cannot scratch it with a knife. This mineral is called quartz.
There are also some little black grains in our chip of granite. If we examine them carefully we find that they can be split into thin scales which are elastic. This mineral is mica.
There is another mineral in granite. It has a light color, but is not glassy like the quartz. It shows bright shining faces. This mineral is called feldspar.
Take a hammer and pound a piece of granite until you have a fine powder. Wash away the dust and mica scales and you will have some clean white sand like that upon the beach.
Nature is breaking the rocks in pieces, but she works quite differently. She takes a long time to make a piece of granite crumble to sand.
The sand which you find by the water's edge is mostly grains of quartz. Quartz is used for making glass.
You will find mica in the brooks in the summer time. When the water is clear you can see the shin ing mica scales moving along the bottom with the current. They look like gold.
Scales of mica are used to make the windows of stoves. These scales are very much larger than those found in granite. Can you think why glass would not do for stove windows? The feldspar in granite finally turns to clay. It is clay that sticks to our feet when it rains. Our china dishes are made from clay.
Bricks are made from sand and clay mixed.
When grains of sand become cemented so as to stick tightly together they form a kind of rock called sandstone. This rock is also used for buildings.
Limestone is still another kind of rock. You can tell limestone because it is quite soft, and when you put drops of an acid upon it little bubbles quickly form. Marble is one kind of limestone. It is used for statues.