[jlrogers (OP)]

I found this rock in the garden while working.  It was almost round and lumpy like a reverse of a golf ball.   I cut it in half and this is what it looks like.  The inside is defiantly less dense in the core. it is not magnetic. 

[jlrogers (OP)]

another

[jlrogers (OP)]

and one more

[RD]

Looks like hexagon at its core ...

 [ Invalid Attachment ]


Thunderegg ?

[JimBob]

Welcome! -- and Thanks for posting

Well, to tell the truth I first thought it was a geode when I looked at the pictures. In fact, it still could be. But being a stickler for details, I know that there must be a source of silica for creating a geode. The definition of thunder egg is different than a geode - http://en.wikipedia.org/wiki/Geode but both require silica.

SOOO ... to help me put the rock in a specific geologic area I did a "tracert" in my Microsoft Command console window for the server in your profile. JL, it shows that you live in the Dallas area. This put this rock in a whole different geologic setting for a geode or thunderegg.

In the Austin Chalk there are many, many pyrite concretions. (The stuff that turns a new white limestone building gray with the passage of time is finely disseminated pyrite.) These concretions can get quite large - several feet long and a foot or two wide. When I was in college in Austin there were many of these brought in to be cut lengthwise as we had a VERY large rock saw at that time. I believe they were found in a large road-cut when the south IH-20 rebuilding construction was being finished.

These large pyrite nodules had been fractured and filled with tan and yellow calcite spar. This looks to be very similar to those. If you look closely in the lower right of the first picture you can see a fracture that can be followed into the core and all the way across it, passing just on the upper side of the clearer crystalline material in the center.

IF you feel you can safely do it, try scratching the yellow-tan stuff with the tip of a knife to see if it will scratch easily. If it does, will the yellow rock slowly fizz in strong vinegar? 

Let us know what happens with your experiment!


Oh - and by the way, how big is it? have a ruler to put beside this? The outlines of the center remind me of a small Brachiopod common in the Upper Cretaceous of Texas. The original center formed the suppoert around which the nodule formed.


frethac - when your at school look in the third floor display cases in the Geology building and take a picture of these on your cell phone.

Gotta brag here - frethac was admitted to the Honors Program At the Jackson School of Geo sciences - WAY TO GO !!!!!!!

[LeeE]

Well done frethack.

[jlrogers (OP)]

Welcome! -- and Thanks for posting

Well, to tell the truth I first thought it was a geode when I looked at the pictures. In fact, it still could be. But being a stickler for details, I know that there must be a source of silica for creating a geode. The definition of thunder egg is different than a geode - newbielink:http://en.wikipedia.org/wiki/Geode [nonactive] but both require silica.

SOOO ... to help me put the rock in a specific geologic area I did a "tracert" in my Microsoft Command console window for the server in your profile. JL, it shows that you live in the Dallas area. This put this rock in a whole different geologic setting for a geode or thunderegg.

In the Austin Chalk there are many, many pyrite concretions. (The stuff that turns a new white limestone building gray with the passage of time is finely disseminated pyrite.) These concretions can get quite large - several feet long and a foot or two wide. When I was in college in Austin there were many of these brought in to be cut lengthwise as we had a VERY large rock saw at that time. I believe they were found in a large road-cut when the south IH-20 rebuilding construction was being finished.

These large pyrite nodules had been fractured and filled with tan and yellow calcite spar. This looks to be very similar to those. If you look closely in the lower right of the first picture you can see a fracture that can be followed into the core and all the way across it, passing just on the upper side of the clearer crystalline material in the center.

IF you feel you can safely do it, try scratching the yellow-tan stuff with the tip of a knife to see if it will scratch easily. If it does, will the yellow rock slowly fizz in strong vinegar? 

Let us know what happens with your experiment!


Oh - and by the way, how big is it? have a ruler to put beside this? The outlines of the center remind me of a small Brachiopod common in the Upper Cretaceous of Texas. The original center formed the suppoert around which the nodule formed.


frethac - when your at school look in the third floor display cases in the Geology building and take a picture of these on your cell phone.

Gotta brag here - frethac was admitted to the Honors Program At the Jackson School of Geo sciences - WAY TO GO !!!!!!!

Jim Bob
thanks for the reply!  I am actually in southern CA but have no idea where the rock came from.  In the house we live in the front flower bed was full of river rocks as decoration.  I found this one mixed in.  it measures about 2.5in in diameter (sorry my tape measure only has in not mm).  I tried placing scrapings from the soft core and the yellow band in the vinegar(5%).   Nothing happened from the soft core scrapings.  the yellow band dissolved and turned a lighter color of yellow.  I thought it was a geode before i opened it but once i did it didn't look like what i expected. 

[JimBob]

(Wellllllll - that is what I get for trusting a Microsoft application --- Actually it is the way the dynamic IP addresses are assigned not Microsoft.)


What I can say is that this is NOT a geode or a thunderegg. The crystal structure of the gray mineral is perpendicular to the center and not layered parallel to the center as in geodes and thundereggs.

I still like the pyrite I.D. for the outer material.

Bass - where are you when we need hand specimen identification??  I am a mud specialist.

[Bass]

JimBob- I think you nailed the identification.

[Geezer]

I am a mud specialist.

JimBob,

Does you mean like one o'thems hipperpotateramuses?

[jlrogers (OP)]

Okay guys... I'm a layperson not a geologist.  I get that you think there is a pyrite exterior and from the color i gather there there is a lot of iron present... BUT is there a name I can post to this "gobstoper"?   I am a simpleton now i love the help and information into a subject i have no experience.   

[JimBob]

You have a -

Pyrite nodule with a calcite core.

Calcite fizzes in 10% HCl.  I was hoping there might be some reaction in a mild acid, vinegar. The fact you can scape things off the crystal at the center means that it is, as you pointed out - soft. Calcite is it. Formed the same way as the Austin Chalk pyrite nodules were formed.

I am a mud specialist.

JimBob,

Does you mean like one o'thems hipperpotateramuses?

No, you hillbilly! Those animals specialize in feces, not sediments.

[frethack]

frethac - when your at school look in the third floor display cases in the Geology building and take a picture of these on your cell phone.

Ill get a picture of it today.  Sorry I havent seen this until now...Ive been swamped with finals/wedding/research.

Gotta brag here - frethac was admitted to the Honors Program At the Jackson School of Geo sciences - WAY TO GO !!!!!!!

Well done frethack.

Thank you very much   Now comes the hard part...completing the honors program...hehehe.

[JimBob]

frethac - when your at school look in the third floor display cases in the Geology building and take a picture of these on your cell phone.

As it has been 40 years. They may not be on display anymore OR the may not be pyrite. Hell, I am getting old. ALMOST as old as Geezer.

And you had damned well better get through the honors program or I will hire some Italians I know to break your knees!

[jlrogers (OP)]

JB,
I take offence to the hilly billy comment! I am one!!!!! []
thanks you for for the information.  is it worth a polish?

[Geezer]

JB,
I take offence to the hilly billy comment! I am one!!!!! []
thanks you for for the information.  is it worth a polish?

Oh, don't you be frettin' thar. Ole JimBob's a hillbilly hiself. He just purtends to have the book lernin.

[JimBob]

That thar be a LYE, Geeze -  Ya'll bein' the hill-er-billy, lvvin' in them thar Selenkirken Mount'ins! I done been from the Hill country ov Texarse! Flatland ifen compared to whar you put yer one room tarpaper hous. And yer heatin' systerm of three hound dogs fer each person in bed on a cold night is jess primer-tive!

JL, no attempt was intended to cast dispersions on you. I have friends who are hillbillies, my sister married one.

WRT the nodule -I would respectfully suggest that if you do decide to polish said nodule, which would to me be a very attractive proposition, that it would be highly prudent on your part to preserve such handwork with a air-sealing coat of clear varnish or polyurethane. Attention should be paid to sealing ALL potential orifices of the nodule half (or both halves) so processed. To achieve this, all surfaces of the half should be coated with special attention addressed to small cracks and holes which at first may not be evident. Without such protection, oxidation and thus dulling of the pyrite will rapidly progress once a glossy state is achieved by such diligent labors as you propose to attempt.

Such extreme dedication to your craftsmanship is highly admirable and I congratulate your diligence, thought and high ideals.   

Please advise us of the progress and the results of your labors.

Kindest Regards,
JamesRobert