Wendall Gardner, age 13, of McAllen, Tex., for his question:
HOW WAS GRANITE FORMED?
Granite is a hard crystalline rock made up chiefly of mineral crystals such as quartz and feldspar and a few dark colored minerals. All granite was once melted rock, like lava. It did not come up to the earth's surface as a liquid, but hardened and formed deep under the ground.
When it was in its liquid state, the granite cooled slowly and thus had time to form fairly large crystals as it hardened. Where such lava poured out on the surface, it cooled so quickly that it did not have time to form large crystals.
Some lava now forms a rock that is so finely grained that its crystals can be seen only through a microscope. This sort of lava is called rhyolite. A chemical analysis will show that rhyolite is the same as granite. Only its physical structure is different.
In many parts of the United States, Canada and elsewhere, geological upheavals in past ages have brought the granite from deep in the earth to near the surface where it now is broken or blasted out in quarries or deep pits.
Granite is light colored and its crystals are large enough to be seen with the naked eye. One can study them on the polished surfaces of granite blocks used in monuments or buildings. The quartz is transparent, much like glass. The feldspar crystals are more or less rectangular and are a dull white color or gray or pink, like fine porcelain.
On a natural broken granite surface, the feldspar grains are so smooth that they are able to reflect sunlight.
The quartz grains do not break along smooth, plain surfaces like the feldspar. The dark colored materials, chiefly black mica and hornblende, are scattered in the mass of quartz and feldspar crystals.
Individual crystals in most granite measures from one sixteenth to one half inch wide. Some granite is coarse grained.
Granite is used for monuments because it can be polished, is hard and is not easily damaged. Carvings and inscriptions on granite withstand weather for hundreds of years.
Much granite is used in the construction of bridges and buildings. It is valuable as a support where great strength is needed because granite can withstand pressure of 15,000 to 20,000 pounds per square inch.
Granite is quarried in more than half of the states of the United States. The leading states include Georgia, Maryland, Massachusetts, Minnesota, New Hampshire, New Mexico, North Carolina, Pennsylvania, Rhode Island, South Dakota, Texas and Vermont.
Many Western states produce granite for local use only because its heavy weight makes transportation costs high.
Quarry men and builders also often use the name "granite" for other rocks which resemeble granite but are composed and constructed differently.
Several other countries, including Canada, quarry granite and the U.S. imports some of their production.