identify this movie - Black rocks that kill people

Monolith Monsters from 1957 fits your description. I have not seen it, but it is part of a giant SciFi movie collection from Amazon.

Here's the blurb from Amazon:

In a desperate race against time and nature, a geologist and a scientist must find a way to stop effects of killer outer-space rocks that are literally petrifying people with fear!

That led me to the IMDB entry and description.

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