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In this typical image of rock fracturing, why do the joints / fissures occur where they do, as opposed to, say, along the line drawn in blue on the image? More specifically, what characteristics of the rock grains on the separated joint surfaces result in a (relatively) planar joint surface?

enter image description here

Glorfindel
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charlie_sar
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  • perhaps getting closer... "microfractures form in a process zone ahead of a propagating macrofracture." So basically a large fracture forms by connecting smaller cracks in the rock ahead of it. But again, why in such a regularly linear/planar fashion? This would seem to imply that all the microfractures are magically lined up in a plane originally. – charlie_sar Apr 05 '22 at 00:41
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    Reg your comment: no, same alignated fracture may occur also in metal materials, micro fracture can be randomly oriented. For example, if you generate voids inside the materials, then you still get a planar/linear fracture: https://www.researchgate.net/profile/Shakir-Gatea/publication/319937742/figure/fig1/AS:549392810561536@1507996861298/Schematic-of-nucleation-growth-and-coalescence-of-voids.png – EarlGrey Apr 05 '22 at 14:29
  • "No" what? the graphic you cite illustrates my hypothesis; the voids that develop are pre-aligned in a linear / planar fashion (from the very first step), then the fracture propagates along that plane. – charlie_sar Apr 11 '22 at 14:35
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    no to "microfractures are magically aligned in a plane". They are distributed in the media, most likely with no dominant orientation, but their cumulative effect may results in the creation of empty volumes which are then "oriented" due to the interaction with the load acting on the rock at that time. What you are asking can be explained with fracture mechanics, therefore by a specialist with knowledge which is acquired at PhD level... and on top of that you need very good skills at teaching and condensing it in an answer of readable size: sorry I am only 2/3 up to the task :) – EarlGrey Apr 11 '22 at 15:02
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    please take all I wrote as "empty volumes" and "oriented" as broad approximation of reality, there is no exact knowledge in those wordings. – EarlGrey Apr 11 '22 at 15:04

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