Michael Merrick, age 10, of Houston, Tex
What is feldspar made from?
Every good cook has a basic recipe for cookies. To this basic recipe she may add ginger, nuts, raisins, chocolate or other goodies to make a wide variety of fancy cookies, So it is with feldspar, the moat plentiful mineral in the earthts crust. A young rock hound may find that six out of ten of his mineral samples are varieties of feldspar, for this mineral, with its many variations, makes up 60% of the earthts crust.
All the various feldspar minerals in the earths crust are silicates. And silicates are compounds of the elements silicon and oxygen. Each basic particle of feldspar contains three atoms of silicon‑and eightatoms of oxygen, plus one atom of aluminum, The trace of aluminum makes feldspar a silicate of aluminum. Chemically, it is a friendly compound, willing to form compounds with atoms of other elements.
One or more atoms of sodium, potassium or calcium may be added to basic feldspar without changing the general nature of the mineral compound, his is why we find so many different varieties of feldspar. Most of the common varieties are pale grey or whitish atone, rough, hard and heavy. They suggest the original meaning of feldspars which is fieldstone. Like many common stones, however, feldspar has its glamorous varieties. Moonstone is a crystal form of feldspar. Labradorite is peacock blue with a waxy sheen. Other varieties are pastel blue or green or chocolate brown.
The various feldspar compounds were formed by seething volcanoes and by the heat and pressure of violent upheavals in the earth’s crust. We find them in granites, gneisses and lava rocks. From birth, they wage an endless warfare with wind, weather and running water.
They may endure for millions of years, but finally they are broken down to fragments of soil and clay, Some feldspars return potassium# which is necessary to plant life, to the soil. Some feldspar forms kaolin, the clay used for making pottery. Natural feldspar is mined and used for ceramics, certain types of glass and glazes for tiles,
Some experts divide the varieties of feldspar into five classes, depending upon the minerals added to the basic compound of aluminum silicate. The class of orthoclase feldspars contains potassium, The albrite class contains sodium. The anorthite class contains calcium in addition to the basic silicate of aluminum. Class fours the alkali feldspars, are mixtures of classes one and two. Class five, the plagioclase feldspars are mixtures of classes two and three.