Jean ruthkowski, age 10, of rochester, n:y:f for her question:

What is Feldspar?

Feldspar is a strong mineral. If you go rock hunting, chances are that most of Your specimens will be made of feldspar, or fieldstone. But in a dozen specimens of Feldspar, no two may be exactly alike, however, they have enough features in common To be classed as different varieties of the same mineral.   The earth has been producing layers of feldspar for some four billion years. And the fob is still going on. At least 60% of the earth's crust is made from feldspar Of one sort or another. It comes in different shapes and colors, but the basic Ingredients in all feldspar are aluminum, silicon and oxygen. It is called one of the Aluminum silicate minerals. Most feldspar 1s rough, granular stone, often sheared at sharp right angles. It Is a lightweight stone, about two and a half times heavier than water. On the scale Of mineral hardness, it rates about six. This means a piece of feldspar can be used To scratch the softer mineral fluorite in class four, and the flourite cannot scratch It back. Feldspar can be scratched by quartz, which is in class seven, but feldspar Cannot scratch quartz.

Feldspar comes in all of the pastel colors, and some of it is fine enough to be cut and polished and sold as semi precious moonstones. The different colors and qualities of feldspar depend upon the ingredients mixed with the basic aluminum silicate. It may contain soda, potash or lime in various amounts and mixtures. The ingredients of feldspar come together in the seething cauldron of volcanic activity. The mixture is brewed under terrific heat and pressure deep within the crust of the earth. It comes streaming forth in rivers of molten lava and finally cools to form a new layer of rocky mineral on the surface of the earth. Feldspar is present in most fire formed rocks, such as granites, gneisses and lavas.

In time, feldspar crumbles to dust and forms clay. Kaolin, the special clay Used to make pottery, comes from feldspar. Lumps of feldspar are smelted to make glazes and enamels. A lot of feldspar is quarried and used as building material.

One of the most common feldspars is microcline, which contains stash. It may be pasty white or pale pink, soft yellow or tinged with blue. Albite is a white or gray feldspar containing sodium. A bluish variety of albite may be cut and polished to make a moonstone. Anorthite is a pale gray or glassy feldspar which contains calcium in addition to the basic ingredients.