Feldspar
From Conservapedia
Of all of the minerals in the Earth's crust, the aluminosilicate, feldspar, is the most common. It is a very useful industrial mineral that finds applications in making glass, plumbing fixtures, tile and pottery. These uses in the United States accounted for about 630,000 ton of U.S. produced feldspar valued at about $27.4 million. It is also a gemstone.[1] Feldspar is number 6 on the Mohs Hardness Scale.
