Thank you very much, metageologist, for responding.
Reading on the internet sure confused me. One article said that granite is useful because its breakdown causes the soil to be alkaline and helps with good plant growth.
thread from AquaticQuotient.com starts off saying that basically all of these responders know that granite is alkaline. There were several such articles with the basic premise that granite increased alkalinity. On the other hand, there were many articles saying the opposite. They supported my opening statement: "Since granite is igneous, I always thought that it didn't have any effect on water chemistry." The part about heavy metals didn't cross my mind though.
I picked up some Muriatic Acid a little while ago and I'm going to pour some on a few of my granite rocks and see what happens.
This is interesting. My granite rocks are combinations of dark gray areas and white areas that are mottled in appearance. These rocks also have some white stripes in them. The white stripes fizzed when I poured Muriatic Acid on them. As an estimate, these white stripes make up less than 2% of the whole rock.
There is a gravel road near me. The granite gravel is basically all dark gray and white colors mixed together. I poured my MA in many spots and nothing fizzed.
This was fun. I live near the Uwharrie Mountains