I watched a Black & White movie on TV. It looked like it could be from 60's. There were some black rock killing people. I only remember one or two scenes. One where a scientist is running some tests and the rocks get water on them and they become animated and kill him. Another scene where a little girl finds some of the black rocks while on a school trip.
Monolith Monsters from 1957 fits your description. I have not seen it, but it is part of a giant SciFi movie collection from Amazon.