In many of my articles, I refer to rock names, especially igneous rocks, those produced from magma and volcanoes.
Igneous rocks are classified on the basis of texture, mineral composition, and chemical composition. Sedimentary rocks are classified mainly by composition and grain size, and metamorphic rocks, mainly by mineral composition and texture. The naming conventions can get very complicated and controversial.
The most practical classification systems, in my opinion, the ones I actually used in the field and laboratory, are the systems devised by Russell Travis (Classification of Rocks, Quarterly of the Colorado School of Mines, vol. 50, No. 1, January, 1955) You can find easily readable Travis charts here:
Igneous rocks:
http://www.kgs.ku.edu/General/Class/igneous.html
Sedimentary rocks:
http://www.kgs.ku.edu/General/Class/sedimentary.html
Metamorphic rocks:
wryheat 