ID Needed, Possible Agate/Fossil ??

[Mnagate34]

I found this while looking for agates in a culvert in Central Minnesota. The backside appears translucent and is mostly smooth to the touch, where the front is not translucent and has a rough texture. There is a sharp needle like pattern that surrounds the middle portion almost like a sagenite agate. I am wondering is it possible for the center portion instead of being filled with quartz like most agates, can this be substituted for a different material? The reason I titled this possible fossil is because it almost looks like some type of worm has been pressed into the design. Any help would be greatly appreciated before I start trying to scratch it or damage it with a test.

 

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[DDancer]

Not a fossil. Not quite an agate either. The center white stone appears to be a close call on jasper and was probably the host rock before fractures in the rock allowed for quartz crystals to form in the fractures. The crystals are quite large but have compacted into what I'd call dog tooth quartz crystals and the layering suggests there were two events where these crystals formed. Agates are formed very similarly however the individual crystals of agate are microscopic in range and have homogenized as the various layers formed much like chalcedony does. These crystals have developed off the original materials seed crystals and grown large. Hints of manganese, iron and a few other minerals have lead to some amethyst and rose colors. Thanks for the natural light photo's as well. Others here might have a better definition for what you have but its unusual and I'd keep it
My opinion anyhow. *grin*

 

[Eu_citzen]

The first set of pics show a breccia, in miniature format. Seeminly is quartz that glued it all together again.

The second stone (is there really two? Looks distinctly different.) I'd call chalcedony.

 

[Mnagate34]

All the photos are of 1 stone. 2 of the photos are of the rock when it is wet, I tried to take as many photos from different angles and lighting. I can see where the outside of the stone might be chalcedony or quartz but I am mostly curious about what is in the middle of the rock on the top side. It is not symmetrical like the needle points that surround the outer edges. I was kind of thinking the top part is limestone because of the rough texture and color but that doesnt give me an answer to what might be the darker color on the top side. I can't help but to see a curled up worm, one end is larger (starts along the outside) than the other giving it an appearance of a tail (ending in the center).

 

[DDancer]

A harness test will help but from what I'm seeing your going to get something harder than limestone. Lime stone is a calcium type deposite and yes silicates can, and do, form in them however its to uniform. Hence I speculate on it being a jasper like base. Also the formations of clear material thru the white material indicate to me that chalcedony or even quartz crystals are present. My thoughts.
EU's analysis has it points as well but I see to much crystallization and the way the material has formed suggests seed crystals and outward development of them from a base structure.
The top developments are of a druzzy quartz to me... small crystal development in a partial vug. For as fractured as the original materiel is that is not surprising but it makes for good development of the overall stone.

 

[Mnagate34]

Thank you everyone for your responses! Definitely helped clear things up for me.

 

[Eu_citzen]

While I agree that the odd formations has to do with crystallization, the white spots likely "healed" fractures (= inclusions), I do disagree that it can't form in breccia zones. Proof is below; a large cavity in a breccia zone, I've been mining faceting material from it for a couple of days now.

Excuse the poor photo, this is inside bedrock, about arms length. I figured I'd photograph the untouched inside, to see if it was viable to keep mining.
Never intended it to be used, but figure this is a perfect example. The breccia is the middle line covered by a little clay and other gooey stuff.

About the same thing happened in your rock, the crystals however didn't have enough space to grow, eventually they "closed" the gap between them, forming a massive vein.

 

[GopherDaGold]

So...not Jesuit?

 

[DDancer]

Been keeping busy EU. Thanks for the pointer. *nods*

 

[Earth]

nice display piece in any case..interesting...