I've been thinking about this "granite" controversy (me arguing with myself, as usual), and what a person might actually get when they purchase a so-called "granite" counter top. Last night I took a look back at one of my beloved geology textbooks for enlightenment, and what did I find?
I know you are just perched on the edge of your seats for this one.
GRANITE DOES EXIST in the IUGS classification scheme.
The what scheme???
The International Union of Geological Sciences has a LOT of diagrams (probably several million, would be my guess) for figuring out how to classify all sorts of rocks. In the case of our granite, the classification covers coarse-grained rocks that cooled underground (as opposed to fine-grained rocks that cooled above ground, such as basalt).
All igneous rocks are classified according to how much of this mineral or how much of that mineral is present. How much alkali feldspar? How much quartz? How much plagioclase? And all these proportions have to be "normalized", and you have to determine the "mode" at which point you determine the "volume percent" of all this plus do some more complicated stuff.
So... Inside one of these multitudinous classification diagrams sits a little area called "granite."
Be that as it may, what a person gets when buying a counter top still most likely will NOT be granite. If it's black it will probably be a gabbro. If it has a lot of light-colored quartz or feldspar it may be a granodiorite or a quartz monzodiorite. OR... it may be something altogether different such as a metamorphic rock!!!
Aren't you glad you asked about granite?
Ya just gotta love geologists. We think this stuff is F-U-N.