rock with crust and contraction cracks

[rockpassion]

Found this rock with a clear crust on it and it has contraction cracks in the crust. And what i have heard from topherspin is that earth rocks do not have contraction cracks. Meteorite or just another boring rock

 

[robertk]

I don't know what makes a contraction crack visibly different from any other crack, so I can't speak to that. But that just looks like a regular Earth rock to me. Whether it's boring or not depends on what rocks you find exciting.

 

[Red-Coat]

If that’s what Topherspin actually said without qualification, then it’s not correct… or you are quoting him out of context. Of course Earth rocks can exhibit contraction cracks. Putting aside sedimentary rocks, where it’s commonly associated with syneresis or dehydration during lithification of the sediment, it’s also seen in igneous rocks. Most usually, it’s seen in quartz-rich igneous rocks and can arise during rapid cooling of the magma, or in rocks that have subsequently undergone multiple freeze-thaw cycles.

Quoting from:

“The origin of small cracks in igneous rocks” by A. Nur & G. Simmons in the International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, Volume 7, Issue 3, May 1970 (NB: only the abstract is available for free)

Abstract
The difference in compressional velocities at pressures of 1 atm and 10 kb, a sensitive indicator of microcrack porosity, is closely related to the presence of quartz in many igneous rock samples. The origin of such cracks can be attributed to the relatively high values of thermal expansion and compressibility of quartz. Only few cracks are introduced by drilling in stressed rocks.

https://www.sciencedirect.com/science/article/abs/pii/0148906270900446

And a couple of other papers for you:

 

[rockpassion]

thats what he said on yout

If that’s what Topherspin actually said without qualification, then it’s not correct… or you are quoting him out of context. Of course Earth rocks can exhibit contraction cracks. Putting aside sedimentary rocks, where it’s commonly associated with syneresis or dehydration during lithification of the sediment, it’s also seen in igneous rocks. Most usually, it’s seen in quartz-rich igneous rocks and can arise during rapid cooling of the magma, or in rocks that have subsequently undergone multiple freeze-thaw cycles.

Quoting from:

“The origin of small cracks in igneous rocks” by A. Nur & G. Simmons in the International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, Volume 7, Issue 3, May 1970 (NB: only the abstract is available for free)

Abstract
The difference in compressional velocities at pressures of 1 atm and 10 kb, a sensitive indicator of microcrack porosity, is closely related to the presence of quartz in many igneous rock samples. The origin of such cracks can be attributed to the relatively high values of thermal expansion and compressibility of quartz. Only few cracks are introduced by drilling in stressed rocks.

https://www.sciencedirect.com/science/article/abs/pii/0148906270900446

And a couple of other papers for you:

Thats what topher said on youtube i think the episode of ureilites. but thaks for the info.