Hmm. I tend to think that photos of rocks typically are "photos for photographers"; with a few exceptions dominated by Ansel Adams, it seems to me that civilian viewers aren't much interested in a black-and-white rock, either as a print or in person. That doesn't make the rock a bad subject (nor does it make the viewers a
bloody rotten audience, I suppose), but it says something about the scope of this discussion.
I submit that most viewers have enormous difficulty in the comparativ^W^W^Wfinding the essence of a subject in any black-and-white image, and that as a result, b&w photography is almost inevitably about some combination of (1) overcoming that challenge, (2) preaching to the relatively small choir of monochromophiles, and (3) working to one's own taste rather than to any particular audience. Rocks mostly skip over the first of those items, the third is wholly personal---and so while I'm all for lithotropism, I do think it resides in a specific, fairly insular segment of the photographic dialectic.
More generally, I'm a little suspicious of viewing photography as "reality with constraints". I'm not sure I can articulate a good alternative, but Feininger's idea of focusing (so to speak) on what the subject is, and on what aspects of it fail to be duplicated in the photo, strikes me as needlessly narrowing.
-NT