Greg Roza 
Potassium [PDF ebook] 

Though not available in pure form, potassium is all around us. It can be found in the earth and the oceans, and even in bananas. About 95 percent of the potassium mined today, however, is used in fertilizers. Written for the middle school reader, this is an engaging and accessible explanation of potassium that covers its atomic structure, unique chemical properties, and place in the periodic table.