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.
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.
So much of our cosmological history starts with the much-discussed big bang, but what led up to that cataclysmic moment? And did time even exist back then?