Helium.com | Geology & Geophysics | Understanding the three basic types of rock http://www.helium.com./knowledge/45531-understanding-the-three-basic-types-of-rock.xml Helium.com > Geology & Geophysics > Understanding the three basic types of rock en-us Copyright Helium.com Mon, 05 May 2008 19:39:55 GMT Mon, 05 May 2008 19:39:55 GMT Scientists are people who try to understand the world. When you want to understand a thing, the first step is often to describe it in a way that sh... http://www.helium.com./items/1649714-how-do-you-tell-apart-igneous-sedimentary-and-metamorphic-rocks Fri, 13 Nov 2009 21:57:34