The rock cycle diagram
USGS Mineral Resources On-Line Spatial Data Map (select Geology/geologic map, and any other desired data– sample below)
Mineral and Rock Identification Made Easy
North East rock types/examples: http://www.pitt.edu/~cejones/GeoImages/index.html
Some rocks split better than others. The quality of splitting is based on the grain or crystalline structure and cleavage planes that should be followed/mimicked when drilling- cleavages are perfect, imperfect, distinct, good, fair, and poor. The difficulty of splitting is formally is described as easy, hard, and difficult to produce.
|1||Basal or pinacoidal|
|3 at 90 degrees||Cubic|
|3 not @ 90 degrees||Rhombohedral|