If I dig up a given rock, make a 3d model of it, and compare that model with those of a large number of other rocks from the same area, what fraction of other rocks would have the same 3d model?

Let's say that the measurement is performed with an accuracy relative to the size of the rock, so a rock that fits within a 100cm sphere might be measured to within the nearest centimeter.

It would be fine to only look at rocks that have been through similar geological processes, rather than all rocks in an area.

I'm broadly interested in an answer for all land areas on Earth, but if there's data for some small region, or theories about rock shape that allow estimating the average entropy, that would be a useful answer.

  • $\begingroup$ The shape of the rock you dig up depends on how you dig it up. It has rather little to do with the type of rock so this seems like a pointless exercise. $\endgroup$
    – bon
    Feb 2 '18 at 23:02
  • 1
    $\begingroup$ @bon I disagree. Foliated rocks will have a distinct shape. This is precisely why they're using phyllites and slates for roofing! Also rocks in the same location will experience the same stress, forming parallel or conjugate joints making them blocky in a somewhat similar way. Same climate will cause weathering of rocks in a similar way (think exfoliating in granites). The shape of rocks on the surface is not random at all. $\endgroup$
    – Gimelist
    Feb 3 '18 at 13:17
  • $\begingroup$ @Michael I agree that the shape of rocks on the surface is not random, but that's not how I interpreted the OP's question. Maybe got the wrong end of the stick though. I still think it's a pointless task. $\endgroup$
    – bon
    Feb 3 '18 at 13:26
  • $\begingroup$ The composition of a rock may affect its texture, but everything else is down to erosion. $\endgroup$
    – Spencer
    Feb 3 '18 at 21:31
  • $\begingroup$ I was thinking specifically of rocks that are not broken off of some larger mass by the method of diggging them up. $\endgroup$
    – Joey
    Mar 15 '18 at 19:29

This would actually be an interesting research project. The ability to do a 3-D scan and model of a rock's shape in a manner that is fast enough to get a statistically meaningful number of rocks measured is relatively new. Certainly you can easily name things that probably control the shape of rocks (lithology, mode of erosion, mode of transport, history of these things) but saying something about this in a quantitative way has not been done AFAIK.

I think this is the sort of question that might result in surprising insights. Or it might lead nowhere. Certainly the question 'Does arid region erosion result in different shaped rocks than glacial erosion?' answered in a quantitative way sounds worthwhile to me.

  • $\begingroup$ I agree with this but it doesn't say anything about the entropy. Quantifying the entropy seems to be a pointless endeavour to me. $\endgroup$
    – bon
    Feb 5 '18 at 18:08
  • $\begingroup$ I've marked this as an answer because knowing that this has not been studied in a way that allows quantifying it is kind of an answer. I would still be interested in better answers of course. $\endgroup$
    – Joey
    Mar 15 '18 at 19:44

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