As part of our geology study we went to a local rock and mineral show. It is a great opportunity to collect minerals and to see where locally people are finding them. This is our first visit to one of theses shows; someone on the AtHomeScience Yahoo group suggested this wonderful idea.
Any child that went to the show got a grab bag of various rocks, and then my kids bought a few, too. The 5 rocks along the bottom of the picture were bought while the rest came in their grab bags.
Ds#1 noticed that one dealer was selling rocks that looked very similar to one he had recently found. We knew it was an igneous rock, granite in particular. It had no pick feldspar though it can be white. The specimen is striking for the many black crystals in it. The black crystals turn out to be biotite, a type of mica; we could tell because it was easy to flake. And since the rock also has muscovite mica, it is called binary granite.
BTW, the University of Pittsburgh and Cal Poly Pomona have informative and pictorial sites for identifying igneous, metamorphic, and sedimentary rocks.