How are rocks made?

Rocks are found almost everywhere.  Very small rocks are called sand.  Rocks bigger than sand have other names, like pebbles, or stone.  Big rocks are called boulders.  In fact, almost all the earth – the mountains and the ground itself – is made of rock.

Rocks are made of minerals.  A few are made of just one mineral, but most rocks are made of many minerals, of magma, that lies under the earth’s crust.  As the magma pushes to the surface of the earth.  It cools and hardens into such rocks as granite, basalt and lava.

Some rocks are formed from bits and pieces of older rocks that pile up in layers and harden into rocks we know as sandstone and limestone.  Still other rocks began as one kind of rock and later were changed into other kinds of rocks.  Some limestone, for example, was changed by hear and pressure deep down in the earth into marble.

What is cement made of?

People often misuse the words cement and concrete.  For example a “cement sidewalk” is really made of concrete.

Cement is the fine, gray powder that is mixed with water, sand and crushed rock or gravel to make concrete.  The cement and water from a paste that hardens as it dries, and binds the sand and gravel together into the hard, rock-like mass we use in building tail skyscrapers, smooth sidewalks and large bridges and dams.

Cement

Cement is made from lime and other materials, such as silica, alumina, iron and gypsum.   The lime used to make cement comes mainly from a rock called limestone.

Cement is made by burning crushed limestone with the other materials.  The heat changes the mixture into a new material called “clinkers.”  The clinkers are then finely ground into the gray, powdery cement.  After this, it is ready for use in masking concrete.

Before the concrete is mixed, workmen must measure the proper amounts of sand, gravel and water with the cement to give it the proper strength.  When first mixed, the wet concrete, called a “batch,” can be poured into molds of almost any shape.  It quickly hardens into a solid mass as hard as natural stone. – Dick Rogers