Agatized gastropods from Morocco

Recently there have been fossilized gastropods replaced with Agate coming out of Morocco. Most are unlabelled or have incorrect names but all are said to be from the Eocene. Below are three different specimens that I believe are all Cerithium sp. based on a little searching and some help from my friend Gery in France.

Specimen #1 profile

View looking down the shell

View of the bottom

Specimen #2 profile

View looking down the shell

View of the bottom

Specimen #3 profile

View looking down the shell

View of the bottom

Gery has collected Cerithium sp. from the Eocene aged sediments of the Paris basin (Bartonian stage). He gave me a couple of websites that had visual catalogs of the different gastropod species that are found in that formation. The first link has a Cerithium tuberculosum (which looks to be very similar to the third specimen above) as the second fossil in the left hand column. The second link has similar shells presented although you have to search a little more as they are not in alphabetical order. It does show a Cerithium tiarella that looks very similar to the first two specimens above. Here is an image of an impressive Cerithium tiarella from Flicker.

Indonesian Agatized Coral

Recently, while trolling E-bay looking for ways to throw my money away, I came across some agatized coral from Indonesia. I won one auction of some end pieces which is good because this way I could see the cross section of the cut fossil and the exposed, weathered end. This allows better study and understanding of the fossil, in my opinion, and makes a nice shelf rock. Lay it with the cut side flat and when someone picks up the seemingly dull piece they are surprised with the detailed interior.

It's hard to find any good information on the age or species of these corals but I know they come from the Island of Sumatra in Indonesia. I would guess that the age is Pliocene to Pleistocene as the island is not that old geologically speaking.






This piece caught my eye because the pattern looks just like a lot of cabochons and polished stones that I've seen at the shows lately. I think they tend to dye this material as the natural color is rather dull.





Simlar structures but smaller in this piece.









This website has a good explanation of how the coral heads are found and processed: http://www.indonesianfossilcoral.com/

Agatized Coral

On a trip to Colorado in 2008 I was looking for agates in an area south of Dinosaur National Monument. The rocks in this area were Devonian to Pennsylvanian in age, according to the geological map, and I was finding lots of broken pieces of a dark red jasper/agate. Then I looked down at my feet and saw this odd looking rock:




It is a colonial tabulate coral that is partially replaced with the red agate. The agate has replaced some areas of the coral and you can see beautiful sweeping curves and lines. In the areas that have not been replaced, the original light gray limestone/calcite preservation of the coral remains giving the piece some character.





It's like parts of the coral have been cut away to allow us study the internal structures more easily. It's too bad that the individual corallites are too small and weathered to really allow more detailed study to determine species. At this point I would say this fossil is part of the family Favositidae.

"Blue Forest"

The Blue Forest is an area in the Eden Valley region of Wyoming where spectacularly preserved petrified wood can be found. The directions to get there are a bit winding and once you get there you may be a little confused by the relatively flat terrain.

View of the area




It's called the Blue Forest because the fossils are often preserved with a ring of blue chalcedony around a gray/black opal replaced fossil wood. You can see piles of dirt and the holes the came from all over the nearby area. You can search the surface and dirt/rock piles for shards of discarded fossil wood/agate but to find whole branches or trunks of wood you have to dig into the rock layers beneath your feet.

A typical trench/hole:


Millions of years ago this area was a seasonal swamp that was part of the ancient Lake Gosiute. Logs and branches would fall into the water and sink to the bottom but were not always quickly buried. The wood became waterlogged and algae would grow on the surface forming Stromatolite like coatings. Eventually both the algae and wood were buried and became replaced with Silica percolating through the ground water. When you are digging you'll find the Stromatolite layers first but you don't know how big a piece of wood you've found yet because the layers thickness can vary.

Here you can see thick layers of Stromatolite that built up on a thin branch.


Experience will help you determine how best to dig out the fossils and how thick a piece of wood you have under all the layers of Stromatolite. Once you get the fossils out of the ground they will cut and polish very nicely since it's agate.




I've not stayed at the site of the Blue Forest long enough to try my had at extensive digging but here is a picture of some pieces of wood I found on the surface.

"Turritella Agate"

"Turritella Agate" is a well known and popular stone that is composed of the fossil shells of a high spired snail called Elimia tenera. The name Turritella is given to the fossils because it looks similar to that family of gastropods, but they are confined to salt water whereas these snails lived in fresh water. The agate itself is considered to be a slightly to completely chalcedonized coquinite.

Here is a polished piece:


The rock formed along the edge of ancient Lake Gosiute and is part of the Green River formation. The accumulations of all these shells must represent a very productive ecosystem and is known to occur in several different stratigraphic horizons within the formation.

I had the opportunity to collect some of the rough stone during a trip a few years back. The best area to collect is south of Wamsutter, WY along the rim of a regional cliff system.



There are lots of small pieces scattered around that are perfect for kids or specimen hunting.



Some of the individual snail shells have weathered out and are available for surface picking.



The material that makes for the best displays has the snail shells oriented parallel to the display surface like in the first polished picture or the field picture below of a rough specimen.



If you cut the rock perpendicular to the shells, this is the view you are likely to get:



The trip to the site was fun and full of nice badland like scenery. A visit can be accomplished with only an hour or so drive from Interstate 80 and makes for a good rest stop when crossing Wyoming either to or from Kemmerer.