Jack Alkire, age 13, of Rock Island, I11., for his question:
WHAT IS FELDSPAR?
Feldspar is the most abundant mineral in the rocks that are found at and near the earth's surface. This group of minerals usually occur as glassy white, reddish, bluish or greenish crystals.
All feldspars contain aluminum and silica, but the varieties differ in the amounts and kinds of other elements that are present.
Microcline, orthoclase and sanidine are called alkali feldspars. They contain sodium and potassium in various amounts. Amazon stone, a green alkali feldspar, can be cut and polished to make jewelry. Moonstone is a milky translucent alkali feldspar that is also a gem stone.
Rocks containing feldspar weather or decompose when they are exposed to the atmosphere. They break down into other minerals, especially the clay minerals. Much of the potassium is held in the weathered rocks and in the soil. These rocks are the chief source for the potassium which all plants need for growth.
Pottery manufacturers use much feldspar. They use the clay materials formed by weathered feldspar to make porcelain and glass. Kaolin, the most important of these clasy, is the chief material used in making high grade chinaware.
Kaolin is actually a pure white clay that is made of feldspar which has decomposed. It contains silica, alumina and water. It can be ground into fine powder. Kaolin is a Chinese word that means "high hill." Kaolin is also called China clay and porcelain clay.
Feldspar is mined almost entirely from bodies of pegmatite, a special kind of rock that contains large crystals of quartz and feldspar. In the United States, feldspar is mined in California, Connecticut, North Carolina and South Carolina.
Slabs of certain types of feldspar are used by architects to face buildings because the slabs contain crystals that give the rock a very ornamental look.
Important kaolin producing countries include the United States, Great Britain, France and Germany. Kaolin producing states include Georgia, South Carolina, Pennsylvania, Florida and North Carolina.
Kaolin is either mined dry with a shovel or dislodged with jets of water and sucked into a pump system. Then it is washed and put through separation processes to remove sand, mica and iron oxide impurities. Excess water is then removed and the clay is formed into cakes that are dried and shipped to potteries.
Kaolin is also used in Textiles, as a coating for paper and as a filler for rubber tires.
Granite is a hard crystalline rock, made up chiefly of mineral crystals such as quartz and feldspar and a few dark colored minerals.
The quartz is transparent, much like glass. The feldspar crystals are more or less rectangular and are colored a dull white, gray or pink, like fine porcelain.