BLT Posted July 20, 2018 Share Posted July 20, 2018 Hello, I have a rather large rock in my yard (middle Tennessee) which I have always thought was interesting. I’m hoping somebody will let me know which type(s) of rock it is? It has gray and white crystals(?) of some sort on top, along with white streaks running through it. It also has several knobby areas. Are these chert nodules? Any information is appreciated. Thanks! Link to comment Share on other sites More sharing options...
ynot Posted July 20, 2018 Share Posted July 20, 2018 Looks like a weathered limestone. The "nodules" could be concretions or chert (hit them with a hammer to see which is what.) 1 Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
BLT Posted July 20, 2018 Author Share Posted July 20, 2018 I feel a bit foolish for having to ask, but how is hitting them with a hammer going to determine which is which? Link to comment Share on other sites More sharing options...
Raggedy Man Posted July 20, 2018 Share Posted July 20, 2018 3 minutes ago, BLT said: I feel a bit foolish for having to ask, but how is hitting them with a hammer going to determine which is which? Think about it. ...I'm back. Link to comment Share on other sites More sharing options...
FranzBernhard Posted July 20, 2018 Share Posted July 20, 2018 This is a tough one. Could be some fragments of rocks in a fine grained ground mass, aka some sort of matrix-supported conglomerate. The attached figure of a rock sprang immediately into my mind: Clasts of fossiliferous limestone in a fine-grained calcareous sandstone. Not to say that yours is the same, just as an example. Try a scratch test with a nail, try if it bubbles with vinegar or hydrochloric (muriatic) acid, both clasts and matrix at several spots. Franz Bernhard 1 Link to comment Share on other sites More sharing options...
ynot Posted July 20, 2018 Share Posted July 20, 2018 6 minutes ago, FranzBernhard said: a scratch test with a nail, The "hardness" test applies to minerals and does not work for rocks. Most rocks are made from different minerals with variable hardnesses. 24 minutes ago, BLT said: I feel a bit foolish for having to ask, but how is hitting them with a hammer going to determine which is which? Chert is much harder than iron concretions. They also break in very different ways. 1 Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
FranzBernhard Posted July 20, 2018 Share Posted July 20, 2018 1 minute ago, ynot said: The "hardness" test applies to minerals and does not work for rocks. Most rocks are made from different minerals with variable hardnesses. Thats correct! I thought it is nevertheless possible to distinguish chert (where you can leave a metallic trace of an iron nail) from iron concretions etc. (where an iron nail would leave a scratch). Franz Bernhard 1 Link to comment Share on other sites More sharing options...
ynot Posted July 20, 2018 Share Posted July 20, 2018 4 minutes ago, FranzBernhard said: Thats correct! I thought it is nevertheless possible to distinguish chert (where you can leave a metallic trace of an iron nail) from iron concretions etc. (where an iron nail would leave a scratch). Franz Bernhard Yes, but both are minerals- one is silicate the other is iron. Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
BLT Posted July 20, 2018 Author Share Posted July 20, 2018 Thanks for the information, @FranzBernhard, @ynot! I took pics of one side of the rock. I will try the scratch test and the vinegar test later. Link to comment Share on other sites More sharing options...
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