Feldspar Feldspar Feldspars (KAlSiO – NaAlSiO – CaAlSiO) are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight. Feldspars crystallize from magma as veins in both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar (see below) is known as anorthosite. Feldspars are also found in many types of sedimentary rocks. The name "feldspar" derives from the German "Feldspat", a compound of the words "Feld", "field", and "Spat", "a rock that does not contain ore". The change from
The Menace from Earth The Menace from Earth "The Menace From Earth" is a science fiction short story by American writer Robert A. Heinlein, first published in the August 1957 issue of "The Magazine of Fantasy & Science Fiction". The story is set in the near future, when the Moon is colonized with people living in underground cities. The "menace" of the title is a glamorous woman tourist who visits the Moon colony. She is assigned a young guide named Holly, a 15-year-old girl and aspiring starship designer who is the first-person narrator. Holly's best friend Jeff develops a crush on the "groundhog" visitor,