I'm not saying you're wrong.
This is the first time I've heard of a landscaping place with only one type of rock. Given the terrain around you, I'd make a few phone calls to other area landscaping places.
sorry they have other 'rocks' but the only one i saw that could be used in an aquarium would be river rocks. the other rocks that they had were either a) too huge or b) they were cut into squares or flat to be used as landscape to make walkways
I got 7 to 8 large pieces of granite (volleyball size) from a local quarry for free. Don't know what you are putting them in with but I have them with my 125 mbuna tank. Best thing about granite is algae does not grow on them.
I have also got river rock right out a stream in WVA, but unlike granite algae loves to grow on them.
Do you all know of any fish stores/landscape places that sell large inert/neutral rocks in the DC, VA, MD area?
I went to the local landscape places (Merrifield Garden) here in Northern Virginia and they only had limestone rocks and those would raise my pH in my tank.
I got mine from Southern States on Broad Street in Richmond. They're not huge but great for small tanks. I still wash and boil them to be sure. I think I got blue stone and it does fine. Doesn't leech anything into the water and my bottom feeders love to play around it.