Unusual Rocks. Does anyone know what they are?

[footleg]

A friend who is a diver in Florida pointed me at this picture of some strange rocks found in a new section of underwater passage pushed by someone he knows. He does not consider himself a caver, but seems to dive in pretty serious caves as far as I can see! He asked me if I knew what they were. I'm not sure I do. Has anyone seen anything like this before?

http://www.flickr.com/photos/57599597@N00/2983601367/

You can see a larger copy of the image on Flickr if you click the link above, and then select 'All Sizes' above the picture on the Flickr page.

 

[Les W]

Some sort of scale would be very helpful

 

[Rob]

Some sort of scale would be very helpful

I agree. If on a small scale they could just be classic "popcorn" formations made out of calcite.

 

[graham]

As others have said, scale dependent.

The first thing that comes to mind is that they are "something else" that has had a layer of mineral deposited on it.

 

[Brains]

Bearing in mind the issue of scale, I find these reminicesent of algal colonies except for the absence of light, but they could have formed at a time of lower sea level. However, they do appear even more like sponges, some of which have silica skeletons, and others have calcareous ones. Even if only "sponge" they could have been over grown in mineral. This is all supposition though...

 

[Wolf]

when it is the same as I've seen before, than they are in size of a tennis ball or even slightly bigger and they are made out of a sandstone like material. But I can not say what it is in detail.

Regards
Wolf

 

[dpegg]

Looks a lot like cave pearls to me

more on http://www.goodearthgraphics.com/virtcave/pearls/pearls.html

 

[Elaine]

It would probably be useful to know whether these caves are in sea water or fresh water too.

I expect!

Like Brains said, some algaes grow like that in mounds, and they may have been covered subsequently in deposits of some sort. My geology brain is stirring somewhere within the depths of my memory but I haven't been able to locate it quite yet!

 

[Brains]

Are they sitting in fine soft sediment with the odd lump of ragged rock poking through, or is the substrate hard limestone that is generally well smoothed? If the latter, and they are integral with the bed rock then perhaps a chert type nodule formation, or maybe a series of redox nodules, each centered on a small decomposing organic item - this may give the sandy internal texture described by Wolf.

Although superficially similar in appearance to cave pearls, I think this is unlikely as those are formed by water dripping into shallow pools, causing limestone to accrete to small particles as a "pearl." Cave pearls are also more typically in my experience a collection of well rounded and "polished" grains loosely lieing in a drip pool...

These are from Browns Folly Quarry

 

[JasonL]

hmm..

Thats hard to say.. Its quite difficult for algal colonies to flourish to such an extent.. conditions must be most unique.. such that no other living organisms are there to devour them all.. usually hypersaline conditions.. thats why we don't see much of them anywhere else. The question is.. is it, inorganic or organic, is the texture calcitic, or something else.

i think a much closer look would be good.. it could be anything!

oh yes.. footleg, the 'asparagus'? we've decided its a scleratinian microselena, not quite sure which species, the ornaments are quite weathered, but i've been tasked to return to matienzo to study the beds above and beneath, and take a good look/sample of the coral from the ceiling!

Jason

 

[gus horsley]

I'm wondering if they're some form of mineral concretion similar to manganese nodules found in tropical seas, only calcite in this case.  Are there any water temperature fluctuations involved which could lead to deposition?

 

[footleg]

Some sort of scale would be very helpful

They are about an inch in size apparently. The owner of the photograph says they were told 'basically they get rolled around to form that shape'

I am pretty sure this is in a fresh water spring BTW

 

[Les W]

Sounds like they may be "ooids" or "Pisoids"

 

[RobinGriffiths]

Could be grapestones -
'A cluster of small calcareous pellets or other grains, commonly of sand size, stuck together by incipient cementation shortly after deposition. The cluster has a lumpy outer surface that resembles a bunch of grapes. Grapestones occur in modern carbonate environments, such as on the Bahama Banks. see also bahamite.'

Glossary of Geology By Julia A. Jackson, Robert L Bates, Klaus K. E. Neuendorf, James P. Mehl, American Geological Institute


Robin

 

[Cave_Troll]

My thoughts are that "rock does strange stuff"
eg this stuff down the Berger