Silicon is not found free in nature, but occurs chiefly as the oxide, and as silicates. Sand, quartz, rock crystal, amethyst, agate, flint, jasper, and opal are some of the forms in which the oxide appears. Silicon is prepared com- mercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be pre- pared as a brown powder, which can be easily melted or vaporized.
Crystalline silicon has a metallic luster and grayish color.
The Czochralski process is commonly used to produce single crystals of silicon used for solid-st4te or semiconductor devices. Most acids, except hydrbfluoric, do 'not affeht it. Silicones are important products of silic' on. Silicon is one of man's most useful elements. Silica, as sand, is a principal ingredient of glass, one of the most inexpensive of materials with excellent mechanical, optical, thermal, and electrical properties.