Spicules or calcite crystals

[Deb in Michigan]

Shamlama resurrected some old images for discussion on spicules and hexactinellids.  Here are a couple of photos that might be of interest from devonian sponge ( stromatoporoids) fossils found in Presque Isle County, Michigan and Alpena County, Michigan.  

[Deb in Michigan]

I could not decide if the needle like structures were calcite crystals which sometimes form columns,(poor preservation of details when this happens)  or if they represented some sort of part of interior structure.  the top photo is of one specimen, which was too large to move, the bottom 3 are of a smaller specimen which I have in my possession.   The specimens found in these locations are mostly calcite with sulfides and pyrite as a small percentage of their makeup.  Spicules are not common among stromatoporoids, so perhaps I am actually looking at some form of Devonian calcareous sponges..   your input is valued and appreciated.  Thank you

[Shamalama]

Hi Deb,

 

Those are some great examples of Stromatoporoids which formed mounds rather than encrustations. The rounded bumps on the surface is the prime indicator of those fossils. The columns are part of the structure of the animal I believe.   In the lower Devonian Keyser formation near me, occasionally one finds reefs that are made up of these Stromatoporoids. Here is an example that I have in my garden that shows the same bumpy pattern. 

[Deb in Michigan]

I find many perfectly preserved stromatoporoid specimens here ,   iIwas interested in showing the spicule like structures in the photos in comparison to your resurrected post.... I believe the second specimen in my photos here might have a very bad infestation of some coral such as syringopora ... note the openings in this photo.. you can even see tube like formations in a few places.     thank you!

 

[Deb in Michigan]

note tube exposed  where i have circled it.  

[Shamalama]

A Syringopora type coral could be a possibility, or they could just be artifacts of preservation. Hard to tell from the pics.

[Mark Kmiecik]

The "tubes" may be voids where the organism simply just didn't grow for whatever reason.