# how much entropy is there in the shape of a rock?

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.

• 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. – bon Feb 2 '18 at 23:02
• @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. – Gimelist Feb 3 '18 at 13:17
• @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. – bon Feb 3 '18 at 13:26
• The composition of a rock may affect its texture, but everything else is down to erosion. – Spencer Feb 3 '18 at 21:31
• I was thinking specifically of rocks that are not broken off of some larger mass by the method of diggging them up. – Joey Mar 15 '18 at 19:29