Please help identify this rock -GRAND CANYON-

[vtgoldprospector]

I found it in the Grand Canyon last year 3/4 the way up the west side of a hill (1300-1400' altitude) around 100 miles east of Las Vegas. It's original shape was parabolic as if it was splattered from an event (like a dinner plate). This is just a nice section of it. It was about 14" diameter and about an inch thick in the center. I did find another similar specimen very close by and were both on the surface and both shaped the same. The 3 photos included show the "slag" that was predominantly on the edges, the color and texture of the top as well as the white bottom. Any ideas?

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[Bajahunter]

Check out the thread, Is this flint?
About halfway down someone posted pictures of Florida fossilized coral. It looks very similar to what you found.
They do find coral in the Grand Canyon.
Some corals are shaped like jellyfish.

[vtgoldprospector]

I searched and manually browsed for "Is this flint?" without any luck,,, how about the user that posted it or a link... thanks.

[gord]

any ideas im thinking maybe flint


Starting with post # 11

[vtgoldprospector]

It not metallic. Seems like silica and calcium based. With the texture of the top I guess it could be coral... but both specimens were on the surface, not partially buried in any way as if it was a fossil of any type. A "splattered" event on the hillside supports it's shape on loose soil and why they were parallel to the inclined grade (as if they were deposited onto the existing & current topology, geologically speaking). Both were identical except for the 2nd one was a little smaller estimated 40 feet away..

[vtgoldprospector]

To be clear, this is only a section of the entire find. The white side (bottom) photo shows the curve of its overall parabolic shape (concave) from which the sample was taken.

[Terry Soloman]

Looks like a piece of petrified sand dune..

[vtgoldprospector]

Looks like a piece of petrified sand dune..

I am by no means an expert but I have doubts about that theory. Any other ideas?

[Eu_citzen]

It does look like some kind of chalcedony.

[woof!]

A chunk from a calcareous soil horizon ("caliche") where some of the calcite has crystallized into a semi-transparent form?

--Dave J.

[austin]

Believe it is/was a coral geode. Outer part looks like limestone. If this is right, it is interesting, but not sure about the value. I think that Bajahunter was correct all along.

[vtgoldprospector]

Can someone supply me with links to photos to compare to.. With the chalcedony/coral ideas, it was found in a "cow patty or upside down dinner plate" shape with the dark textured surface face up (slag on the bottom and edges) inverted from what a geode would be. I can believe it may have been a geode at one time but what would explain its current shape? I also question why I found 2 very close to each other without looking very hard. Leads me to believe there were others. For what ever reason I still can't seem to find the thread that Bajahunter was talking about.

[EricTheCat]

I still can't seem to find the thread that Bajahunter was talking about.

Greetings vtgoldprospector,
I think this might be the thread Bajahunter was referencing, link to post #11: any ideas im thinking maybe flint

It does look quite similar to what you found.

[Bajahunter]

Prospector
Gord posted the link to the thread already.
any ideas im thinking maybe flint
The rocks you should look at start at post number 11 in that thread.
They are completely different than the flint/chert rocks that were the original topic.
I can't ID based just on the pics. It does look like some kind of chalcedony to me.
I doubt if it changed shape since it was formed.
Rob

[austin]

Check out coral geode on google images. There are probably many more, some smashed, some still buried. Value?

[Bajahunter]

Here is some more info. From the web site:
Agatized Fossil Coral

In some cases corals were buried in sediment as the land surface was affected by crustal plate movements or the oceans rose and fell. Temperature and pressure from compaction during burial resulted in those deposits becoming rock and part of the present day geological record.

Agate, also known as chalcedony, is a type of cryptocrystalline quartz or silicon dioxide. Under unique geological conditions, prehistoric corals and mollusks can fossilize by being replaced with agate from silica-rich ground water percolating through limestone.

Was this found on a Limestone bed?
Corals come in all kinds of shapes. It might have been squished when it was first buried, but the shape probably didn't change after it was replaced with silicon dioxide.
I have found some rocks similar to yours here in Baja. I never thought along the lines of coral until centfladigger posted his pics of his coral.
If he is here I would be interested in his opinion.
Rob

[vtgoldprospector]

Cryptocrystalline quartz or silicon dioxide would be agreeable on its composition. Very interesting. Thanks for all the input. It was found on a dirt surface face up and clean from debris as if they were getting a tan. They were not near any rock outcrop.

[GatorBoy]

I would almost definitely call that agatized coral. I'm in florida where we have alot. yours happens to be a really nice looking piece. the fact that you found it in the grand canyon is real cool too. we also have a lot of calcite. the only piece of a agatized coral I have at the moment is a really nice projectile point I found in saint lucie county florida. I do believe I have some calcite also.
the first photo is my calcite.

the point is agatized coral.



I have found calcite with a very small crystals that looks similar to your piece. but judging by the size of the original piece that you mentioned I'm leaning towards agatized coral.

[vtgoldprospector]

I showed a guy at a local annual gem & mineral show and he seems to think it is agate quartz. A sample he had was very similar but his quartz was on the interior, opposite from this sample.

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