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Originally Posted by Mercury  I like how you arranged those rocks. BTW, what kind of rocks won't effect hardness and pH? |
Sorry Lakea, I don't mean to hijack your thread.
Carbonate rocks will affect hardness and pH. Limestone for example.
(fyi, sandstone, if it has a carbonate cement, can affect hardness and pH... same for slate/shale. I've collected sandstone and shale/slate samples for school that had a carbonate/dolomite cement.) Doing the 'vinegar test' should tell you if it has a high concentration of carbonates. Hydrochloric acid will tell you if there's even a little... of course, not everyone can readily get their hands on HCl
Igneous rocks definitely shouldn't affect your pH (granite, scoria [lava rock])
Oh, how I just love rocks!