Macaronifeather Posted June 27, 2016 Share Posted June 27, 2016 What could this strange rock be? It has striations and Some black stuff. Any thoughts or ideas appreciated. Link to comment Share on other sites More sharing options...
xamageo Posted June 27, 2016 Share Posted June 27, 2016 In my opinion it is a rock Link to comment Share on other sites More sharing options...
doushantuo Posted June 27, 2016 Share Posted June 27, 2016 any chance of the thin black layer being a stylolite,because of it's morphology(thin,more or less zig-zag)? Link to comment Share on other sites More sharing options...
tmaier Posted June 28, 2016 Share Posted June 28, 2016 (edited) In my not so humble opinion, it is limestone, and the end that you are holding upward is the native sediment, and the bottom part has gone through a diagenesis towards becoming dolomite. The black stuff is magnesium, which is reacting with the limestone to transform it from CaCO3 to CaMg(CO3)2. The striations are actually the facets of the growing dolomite crystals. Edited June 28, 2016 by tmaier 1 Link to comment Share on other sites More sharing options...
CraigHyatt Posted June 28, 2016 Share Posted June 28, 2016 In my not so humble opinion, it is limestone, and the end that you are holding upward is the native sediment, and the bottom part has gone through a diagenesis towards becoming dolomite. The black stuff is magnesium, which is reacting with the limestone to transform it from CaCO3 to CaMg(CO3)2. The striations are actually the facets of the growing dolomite crystals. I'm glad you piped up tmaier, because I had some questions. My first thought was crystals, but I noticed some banding or texture that's orthogonal to the apparent growth. Because that horizontal texture is visible in the white material, it almost looks like the white material is flowed onto the substrate--the sort of thing you see in cave formations. I was thinking that crystals should look a bit more regular and they should just do their own thing regardless of the substrate texture. Of course all of this assumes the horizontal banding happened first, but it looks like it based on the yellow bands near the top of the photo. Thoughts? Info: Craig Hyatt, retired software/electrical engineer Experience: Beginner, fossil hunting less than a year Location: Eagle Pass, TX USA on the border with Mexico, hot dry desert Formation: Escondido, Marine, Upper Cretaceous Materials: Sandstone, Mudstone, Shale, Chert, Chalk Typical: Thalassinoides, Sphenodiscus, Exogyra, Inoceramus Reference: http://txfossils.com/Txfossils.html Link to comment Share on other sites More sharing options...
doushantuo Posted June 28, 2016 Share Posted June 28, 2016 (edited) Correct me if I ám wrong but stylolites and dolomite often go together,don't they? Pressure solution<->diagenesis The stylolitic seams could/might be filled with a magnesium rich clay,perhaps montmorillonite? Edited June 28, 2016 by doushantuo Link to comment Share on other sites More sharing options...
CraigHyatt Posted June 28, 2016 Share Posted June 28, 2016 any chance of the thin black layer being a stylolite,because of it's morphology(thin,more or less zig-zag)? After first searching styolite to see what that is.... I think it might not be, because the fracture seems to extend straight down on one end. Or maybe it's a segment of a styolite, and the other fractures happened later. This chunk of rock is a great geology lesson. :-) 1 Info: Craig Hyatt, retired software/electrical engineer Experience: Beginner, fossil hunting less than a year Location: Eagle Pass, TX USA on the border with Mexico, hot dry desert Formation: Escondido, Marine, Upper Cretaceous Materials: Sandstone, Mudstone, Shale, Chert, Chalk Typical: Thalassinoides, Sphenodiscus, Exogyra, Inoceramus Reference: http://txfossils.com/Txfossils.html Link to comment Share on other sites More sharing options...
doushantuo Posted June 28, 2016 Share Posted June 28, 2016 (edited) Stylolites form at lithological discontinuities(carbonate grainsize might control compaction and/or dissolution)............... Edited June 28, 2016 by doushantuo Link to comment Share on other sites More sharing options...
tmaier Posted June 28, 2016 Share Posted June 28, 2016 This could be formed from a cave, and water and maybe pressure was likely involved, causing the banding that you see. Crystals don't often get a perfect environment for growth, so they aren't always perfect or regular. I think the banding that you see is staining, maybe from the mineral form of magnesium. If one end is limestone and the other end dolomite, then vinegar will fizz on the limestone end and will not fizz on the dolomite end. 3 Link to comment Share on other sites More sharing options...
doushantuo Posted June 28, 2016 Share Posted June 28, 2016 look at figure 6 in this one http://uu.diva-portal.org/smash/get/diva2:827283/FULLTEXT01.pdf ,and the third pic from the left. 1 Link to comment Share on other sites More sharing options...
howard_l Posted June 28, 2016 Share Posted June 28, 2016 It is a stylolite, they are very common in Silurian, Devonian and Mississippian age limestones and dolostones in Kentucky. 3 Howard_L http://triloman.wix.com/kentucky-fossils Link to comment Share on other sites More sharing options...
doushantuo Posted June 28, 2016 Share Posted June 28, 2016 (edited) Probably because of the Appalachian orogeny,I suppose(compressional deformation) Large scale tectonics affecting the Great American Carbonate Bank? Edited June 28, 2016 by doushantuo Link to comment Share on other sites More sharing options...
supertramp Posted June 28, 2016 Share Posted June 28, 2016 maybe a slickenside structure on an fragment of an undulated surface? ciao 1 Link to comment Share on other sites More sharing options...
doushantuo Posted June 28, 2016 Share Posted June 28, 2016 I was too obsessed with th stylolite . Good call about the slickensides,Supertramp 1 Link to comment Share on other sites More sharing options...
howard_l Posted June 28, 2016 Share Posted June 28, 2016 Kentucky Stylolites from the Silurian of Buillitt Co. KY 3 Howard_L http://triloman.wix.com/kentucky-fossils Link to comment Share on other sites More sharing options...
supertramp Posted June 30, 2016 Share Posted June 30, 2016 I think you are right howard; looking carefully at the rock, it really seems to be a fragment of a (columnar?) large amplitude stylolite (much less common than low amplitude ones in “my” Apennines), with the striated sides produced by friction during the interpenetration of the interlocked prisms. thank you http://earthinsightcache.blogspot.it/2010/03/weathered-stylolites-in-silurian.html http://www.flickriver.com/photos/chucksutherland/5390340845/ http://www.lakeneosho.org/Russia/Stratig3.html 1 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now