Vermiculite and Perlite

Some of you were asking about two of the ingredients frequently found in potting soils: vermiculite and perlite. Here's a nice article in the Washington Post about the two substances, where they come from, and why you might use them in a seed-starting or potting mix: http://www.washingtonpost.com/lifestyle/home/get-to-know-your-potting-mix-vermiculite-and-perlite/2014/03/25/c0385bf2-add0-11e3-b8b3-44b1d1cd4c1f_story.html