Quartzite, a metamorphic rock derived from sandstone. In some quartzite the sand grains are recemented with silica. In others the metamorphism (change) of the sandstone results from great pressure. Quartzite is extremely hard and highly resistant to chemicals. It has a glassy luster and may be white, gray, pink, or brown. Quartzite is used in making glass and to pave roads.
So much about galaxies remains a mystery. We know what they're made of and that we live in one (the Milky Way), but we're not sure how they form and evolve.
He is famous for a phrase he never said, for wearing turtlenecks and for hosting the original 'Cosmos' TV series. As enthusiastic about the stars as he was about marijuana, Carl Sagan led a very surprising life. Here are 10 cool facts.