ever seen knappable sedimentary rock?

[ozy clint]

i found a piece of rock the other day. it's clearly a sedimentary rock with defined layers but it looks homogeneous. i hit it and a flake busted loose! strange?
i'll have a bit more of a play and get some pics of it.

the flake margins are sharp but not as sharp as normal rock. it's definitely breaking concoidaly.

[makenzie71]

Most people I've talked to about such things say that such stones have been used with success, but they weren't "knapped"...they were ground and polished.

[jcinpc]

Sedimentary rock formation begins with igneous, metamorphic, or other sedimentary rocks. When these rocks are exposed at the earth’s surface they begin the long slow but relentless process of becoming sedimentary rock.

Weathering
All rocks are subject to weathering. Weathering is anything that breaks the rocks into smaller pieces or sediments. This can happen by the forces of like wind, rain, and freezing water.

Deposition
The sediments that form from these actions are often carried to other places by the wind, running water, and gravity. As these forces lose energy the sediments settle out of the air or water. As the settling takes place the rock fragments are graded by size. The larger heavier pieces settle out first. The smallest fragments travel farther and settle out last. This process of settling out is called deposition.

Erosion
The combination of weathering and movement of the resulting sediments is called erosion.

Lithification
Lithification is the changing of sediments into rock. There are two processes involved in this change. They are compaction and cementation.

Compaction
Compaction occurs after the sediments have been deposited. The weight of the sediments squeezes the particles together. As more and more sediments are deposited the weight on the sediments below increases. Waterborne sediments become so tightly squeezed together that most of the water is pushed out. Cementation happens as dissolved minerals become deposited in the spaces between the sediments. These minerals act as glue or cement to bind the sediments together.

The process of sedimentary rock formation takes millions of years to complete only to begin a new cycle of rock formation.

The Rock Cycle

[jcinpc]

I copied that to get myself a clearer definition. ( used for my sons scout project) . My question then is this.. Is this rock I find in a layer deeper than my coral beds , sedimentary?  I find shells that are knappable and what looks like limbs, totaly silicified. this rock or chert or whatever is some type of compressed algea formed when Florida was under water. this stuff is shiny and knaps raw. I dont knap so I couldnt tell you but I do spall alot of it out. I can also cook the lighter colored stuff and get pinkish colors, brown stays brown on this rock. On some pieces you can definatly see the layes and this is found in sheets, not boulders or chunks. Heres some pics of what I`m talking about

[otis.drum]

clint,
my guess would be metamorphic rock.

sedimentry rock can later become metamorphic.

say it originally formed as sedimetry, but was later heated by being in close proximity to lava flow. this changes the rock from sedimentry to metamorphic, and changes its characteristics with it. example are, marble, slate, quartzite.

...."Contact metamorphism is produced by direct heating of rocks around an igneous intrusion"

most knappable rock, i would think, would be igneous, like, basalt, obsidian, granite.

sedimentry are not heat treated in the same way and are, from my understanding, generally softer, like, sandstone, limestone etc

[otis.drum]

sedimentry can also be changed into metamorphic by water (carrying minerals) running through it and depositing the new minerals into the sedimenty rock.

[RidgeRunner]

I am not a flint knapper or a rockolgist.
But, from what little of it I have seen that looks like Coastal Planes Chert to me.

David

[Hillbilly]

Most knappable stone is sedimentary, except for a few exceptions like rhyolite, obsidian, dacite, etc. All cherts and flints are sedimentary rock, along with many other sedimentary or metasedimentary knappables.

[jcinpc]

We dont have coastal plains down this far south, I`m outside of Tampa. This is some type of compressed algea. This rock is only in this 1 location. I have not run across it in my 25 years of digging these area. Kind of like the "ledge Flint" that Rick found on the Alifia river, only found in that 1 location

[mullet]

I've seen some like that Jeff that was Agatized Oyster shells. The first one looks like it might have been some kind of sea sponge, also. And if it ever warms up I'm going to make a run after some ledge.

[ozy clint]

ok guys here's the rock i'm talking about. you can clearly see its layers. notice also how the flake scars have a grainy surface texture. not sure if it will be good for fine work but it might yield a rough tool. would heat treating increase its knappablity? 

[mullet]

 Yes. I think heat treating will help it. You could start out around 550dgs Centigrade and see how that works. As grainy as it looks it might take more. It looks like a grainy chert to me, though. Should work.

[sailordad]

ozy:  if was you i would heat adn try it,cant hurt


jc:  the rock in the 8th and 9th pics of yours,dont know what it is but i think there was some of it in that box i got from you.i like it,it works nice

[ozy clint]

how long should you hold it at that temp?

didn't think there was any knapping rock in australia besides mookite.

[sailordad]

you got mookite?
you lucky dog
i love that stuff