A syringopora (coral)?

[Patek20]

Dear forum members,

 

Here are some items that I found on an island close to Vodice, Croatia, Europe.

The location was ca. 30 meters from the adriatic sea at a hight of ca. 8 meters above sea level.

The items were at the bottom of a building site for a house. They were about 2 meters below ground level, i.e. 6 meters above sea level.

 

Here are two pictures of an item which looks a bit like a coral.

The closest match I found on the internet was the picture depicted on the right hand side of https://en.wikipedia.org/wiki/Syringopora

 

There was an abundance of items like this around the location.

This item has a diameter of ca. 20 cm and a height of ca. 9 cm.

 

 

The mineral seems to be quartz (an uneducated guess).

To show the mineral in a better way, here are pictures of two other items I found at that site.

The one on the left has a length of ca. 10 cm (please ignore the scallop shell), the one on the left more like 7 cm.

 

 

The items are not here with me at the moment, so it would take some effort to get more photos if requested by you.

But it would be manageable.

 

Could you please help to ID this item?

 

 

[TqB]

It's tricky without a definite age. There are similarities with Syringopora (possible sections of infundibuliform tabulae in some of the tubes) but it looks odd.

I think the tubes are a lot wider than typical syringoporids - they seem to be up to 7mm or more (based on 20cm max. diameter for the first photo), and have a much wider variation in diameter than usual.

 

So I'm not sure but feel it's probably not. A good longitudinal section would help..

[Rockwood]

4 hours ago, Patek20 said:

Here are two pictures of an item which looks a bit like a coral.

I see features which seem quite inconsistent with it's being coral at all to me. The tapering and merging in places just seems wrong.

[Patek20]

Thank you for your feedback.

I will try to get hold of a photo with a ruler in it, to show a more accurate size.

It will take a few hours.

[Shamalama]

I'm going to suggest they are speleotherms, structures formed in caves. They look like travertine deposits to me. is the host rock nearby limestone or dolomite?

[Patek20]

Hi Dave,

 

Thank you for your suggestion.

I checked pictures for 'dolomite Croatio' on the web and found:

https://www.dreamstime.com/stock-photo-detail-dolomite-calcite-stone-surface-image27595910

 

This definitely looks like the host rock nearby, there were these concentric quartz-like structures as in the linked picture and the red/brwon colours also agree.

 

For the moment, I cannot get hold of a photo with a ruler, but I received the info on the diameter of the 'branch-like' tubes/cylinders in the first two pictures above:

Typically, they measure as 3-4 millimeters, some go up to 6 mm.

 

Speleothems is a new thought to me.

I found:

https://www.showcaves.com/english/gr/showcaves/AgiosGeorgios.html

and in particular the image on the right hand side,

https://www.showcaves.com/images/Big/D056-1467.jpg

looks similar to the stone that I found.

 

I am just wondering where the cave would have been.

The location where I found the stone next to the coast did not look like a cave at all.

But the present site might have looked very different some million years ago ...

 

[Rockwood]

2 hours ago, Patek20 said:

But the present site might have looked very different some million years ago ..

Think ice age.

[supertramp]

2 hours ago, Patek20 said:

Hi Dave,

 

Thank you for your suggestion.

I checked pictures for 'dolomite Croatio' on the web and found:

https://www.dreamstime.com/stock-photo-detail-dolomite-calcite-stone-surface-image27595910

 

This definitely looks like the host rock nearby, there were these concentric quartz-like structures as in the linked picture and the red/brwon colours also agree.

 

For the moment, I cannot get hold of a photo with a ruler, but I received the info on the diameter of the 'branch-like' tubes/cylinders in the first two pictures above:

Typically, they measure as 3-4 millimeters, some go up to 6 mm.

 

Speleothems is a new thought to me.

I found:

https://www.showcaves.com/english/gr/showcaves/AgiosGeorgios.html

and in particular the image on the right hand side,

https://www.showcaves.com/images/Big/D056-1467.jpg

looks similar to the stone that I found.

 

I am just wondering where the cave would have been.

The location where I found the stone next to the coast did not look like a cave at all.

But the present site might have looked very different some million years ago ...

 

 

Yes, looks like coral, but "cave coral"  (coralloids, coralloid speleothems).
ciao
 

 

[Patek20]

Thank you for all your feedback!

 

Here is my summary hypothesis on what these stones are, also for those who read this post sometime later:

• Each of the stones consists of two parts:
  • A dolomite part with a concentric ring structure (formed more than 100 million years ago).
  • Speleothems consisting of travertine or dolomite, formed in a cave 30 000 - 500 000 years ago.
    • The argument for the speleothems being dolomite would be the colour 'pink' as described at the beginning of https://mostateparks.com/page/55118/speleothems
    • The spelothems being travertine was suggested by Dave above.
• So, it is not a fossil. But since it looks to the untrained eye quite like a coral, it is called 'cave coral'.

The main learning for me was that the stone consists of two parts with substantially different ages.

I had just assumed that it was formed 'in one go' since this is a solid stone.

[Shamalama]

You have done a god job of researching after the clues and suggestions we made. It is always good to learn more. The next time you are there you will have to look and see if you can find more of those formations.

 

From your original post, I see you found them near a site where they are building a house. Those rocks may have been brought in from a quarry to use as a foundation, or they were broken on site to make room for the house. The cave may not have been very large. I have found small (less than 1/2 meter) openings in limestone quarries that have Travertine and other cave formations.

[Patek20]

8 hours ago, Shamalama said:

You have done a god job of researching after the clues and suggestions we made. It is always good to learn more. The next time you are there you will have to look and see if you can find more of those formations.

 

From your original post, I see you found them near a site where they are building a house. Those rocks may have been brought in from a quarry to use as a foundation, or they were broken on site to make room for the house. The cave may not have been very large. I have found small (less than 1/2 meter) openings in limestone quarries that have Travertine and other cave formations.

Thank you for the encouraging feedback and extra info on a potentially smaller cave size!

 

I would have thought that the rocks were broken on site, but as a learning from this posting I should not fully rely on my assumptions.