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Is this a fossilized egg?


PhungHieu

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First, I apologist if my English grammar has problems because I'm not native.

I found it in Binh Thuan, Vietnam which looks very much like a egg fossil.

 

IMAG0100_2.jpgIMAG0097_1.jpgIMAG0102_1.jpg

 

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Welcome to The Fossil Forum!

This is not a fossil egg, it is a volcanic rock called a geode or thunderegg

 

Tony

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The raised seams on the outside suggest a septarian concretion, which had calcite flow through cracks to form the crystals in the middle. Like other concretions, they may be found near fossils and can have formed around them, but usually the interior just has crystal. Very nice specimens though!

 

Example of a septarian concretion:

septarian-concretion.jpg

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8 hours ago, trisk said:

The raised seams on the outside suggest a septarian concretion,

 

3 hours ago, abyssunder said:

That is a really nice septarian concretion/nodule .

This one is NOT a septarian concretion -- it is a geode!/thunderegg..

Pictures of some I have found...

DSCF2080.JPG

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1 hour ago, ynot said:

 

This one is NOT a septarian concretion -- it is a geode!/thunderegg..

Pictures of some I have found...

DSCF2080.JPG

Oh wow, so these are definitely volcanic in origin... not finding much literature on it but I guess a similar mechanism creates the seams in their outer shells as in septarians.

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A septarian forms from shrinking mud.

These are formed from a gas filled silica bubble in lava. when the bubble "pops" it forms the cracks and a hollow center that is held in place by the lava. 

Both are then filled with other minerals. (If they completely fill the void it is called a thunderegg, if it partially fills the cavity then it is called a geode.)

A "geode" from Dugway Utah..

DSCF2093b.jpg

 

A "Thunderegg" from Deming New Mexico.

DSCF4815.JPG

 

Tony

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7 hours ago, ynot said:

 

This one is NOT a septarian concretion -- it is a geode!/thunderegg..

 

Thunderegg is not synonymous with either geode or agate.

No doubt, the exterior side of the specimen in question resembles a septarian type nodule, with the conventional calcite walls and the internal calcite which could fill entirely or partially the "cetral core".

Also, there is another term with the same character, septarian geode .

 

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29 minutes ago, abyssunder said:

Thunderegg is not synonymous with either geode or agate.

No doubt, the exterior side of the specimen in question resembles a septarian type nodule, with the conventional calcite walls and the internal calcite which could fill entirely or partially the "cetral core".

Also, there is another term with the same character, septarian geode .

 

A thunderegg can be hollow (geode) or solid.

A geode can be a thunderegg (with a hollow center) or other crystal lined rocks (coral, septarian...). Agate is just one of many minerals that can fill the space in the rock.

A septarian has a surface that is cracked like dried mud with the crack filling being raised above the enclosing rock. The lithified mud is softer than the mineral filling and will wear down faster than the hard silica shell of a thunderegg. 

A thunderegg has the same elevated filling of the cracks, but the enclosing rock is mounded above the plain of the cracks. The cracks will also have a different geometric pattern than a septarian.

The rock in the OP is definitely a "thunderegg" type of volcanic rock. (since it is hollow I called it a geode).

 

Tony

 

PS I never said anything about it being agate.

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All the images above call the septarian type structure, no matter the way they are supposed to form.
" The process that created the septaria, which characterize septarian concretions, remains a mystery. A number of mechanisms, e.g. the dehydration of clay-rich, gel-rich, or organic-rich cores; shrinkage of the concretion's center; expansion of gases produced by the decay of organic matter; brittle fracturing or shrinkage of the concretion interior by either earthquakes or compaction; and others, have been proposed for the formation of septaria (Pratt 2001). At this time, it is uncertain, which, if any, of these and other proposed mechanisms is responsible for the formation of septaria in septarian concretions (McBride et al. 2003). " - Wikipedia

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I read this somewhere and copied it:

 

"Septarians were formed during the Cretaceous period, 50 to 70 million years ago when the Gulf of Mexico reached what is now Southern Utah. Decomposing sea life killed by volcanic eruptions, had a chemical attraction for the sediment around them, forming mud balls. as the ocean receded, the balls were left to dry and crack. Because of their bentonite content they also shrank at the same time trapping the cracks inside. As decomposed calcite from the shells was carried down into the cracks in the mud balls, calcite crystals formed. A thin wall of calcite was transformed into aragonite separating the bentonite heavy clay exteriors from the calcite centers. Because of this, the nodules are called Septarians." 

There was also something about #seven, average 7 sided formations.

 

Which is pretty much what abbysunder said.

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2 hours ago, Innocentx said:

I read this somewhere and copied it:

 

"Septarians were formed during the Cretaceous period, 50 to 70 million years ago when the Gulf of Mexico reached what is now Southern Utah. Decomposing sea life killed by volcanic eruptions, had a chemical attraction for the sediment around them, forming mud balls. as the ocean receded, the balls were left to dry and crack. Because of their bentonite content they also shrank at the same time trapping the cracks inside. As decomposed calcite from the shells was carried down into the cracks in the mud balls, calcite crystals formed. A thin wall of calcite was transformed into aragonite separating the bentonite heavy clay exteriors from the calcite centers. Because of this, the nodules are called Septarians." 

There was also something about #seven, average 7 sided formations.

 

Which is pretty much what abbysunder said.

 

It is also what I said, to a lesser degree...

 

4 hours ago, ynot said:

A septarian has a surface that is cracked like dried mud with the crack filling being raised above the enclosing rock. The lithified mud is softer than the mineral filling and will wear down faster than the hard silica shell of a thunderegg. 

 

I also said that the OP piece is not a septarian. A septarian nodule is a sedimentary structure, which is different from a thunderegg which is a volcanic structure.

See this site for a comprehensive explanation of the formation of thundereggs. http://www.zianet.com/geodekid/thndregg.htm

 

An excerpt from that site...

   "All base their theories on the assumption that by some force, mechanism or other culminating processes of nature, large cavities were developed in the acid magmas. The cavities are in reality the only basic starting point for every theory known to the author. The interiors of gas cavities are in general very smooth. Unless deformed after formation, the cavity walls have no distortions or irregular interior surfaces. The writer has never seen rough, irregular inside walls in scoria or other rocks with gas cavities large enough for the examination of their inside cavity walls..." 
    Then he concludes: 
    "Hence it must be certain that thundereggs are not casts of gas cavities and all theories based on gas cavity filling must be completely defective..." 
    He goes on to state that, 
    "...even our renowned petrographers and mineralogists have been led astray on fruitless routes by trying to match the spherical shape of thundereggs with that of the gas cavities..." 
    He continues to describe his theory on thunderegg genesis which postulates an accretion of silica gel as an immiscible directly out of molten rock which then spontaneously solidifies to the entities we find today. 
    I must credit this gentleman with piquing my intuition and inspiring me to reevaluate and write about what I have seen in my specimens and how they occur in the field. My first reaction to this "hot gel" theory was to ask how a calcite crystal could get into such a hot environment, become encased and circumscribed with bandings of the agate. Calcite crystals cannot form in the 2000o+ Fahrenheit temperatures in the relatively low pressures of a lava flow. Such temperatures would reduce calcite to calcium oxide and carbon dioxide. I have scores of specimens with calcite crystals well inside the agate, as well as other water-based inclusions such as manganese dendrites, zeolites (sagenite) plumes and stalactitic growths. These growths, which in most cases are the first implacements in thunderegg cavities, have subsequent bandings of chalcedony and/or quartz coating and outlining these as well as every other protuberance on the cavity wall itself. This is why the radial fibrous structures are seen on weathered agate cores of thundereggs which are often mistaken for agate casts of fossils or coral, which we shall be entertained with later. 
    The way the thunderegg shell and cavity develop are totally different from how their contents are implaced. The agate, opal, quartz, jasper, colors, calcite and aragonite, zeolites, dendrites, plumes, bandings, and the inclusion or exclusion of any of the above depending on location, makes for a variety of complex events. So complex that while at the same time Shaub (1979, pages 2352 & 2354 in the same Lapidary Journal quoted above) maintains that thundereggs are formed in their entirety in a "closed system," but dismisses the complexities of that process for another, later study: 
    "The development of the complex interiors of the thundereggs is a long and varied story in itself, a story that was directly involved with the different states and composition of a solution and its crystallization in a closed system above the critical temperature as well as at a somewhat lower value. There is probably no experimental data available that would cover such large masses of material and under such varied compositions. Hence, one must exercise some geological and physical-chemical applications in deducing the probable progressive development of the interiors (a field for different ideas)." 
    Perhaps we can get closer to understanding thundereggs by approaching them as gas cavities filled with water-based minerals, like those of amygdaloids, an idea fairly well accepted by most geologists. 

 

 

3 hours ago, abyssunder said:

 

All the images above call the septarian type structure, no matter the way they are supposed to form.

 

As I said before it is not a septarian nodule

From Wikipedia...

Septarian concretions or septarian nodules, are concretions containing angular cavities or cracks, called "septaria".

A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil.

The pieces that I posted pictures of are self collected thundereggs, they are not septarian nodules. All of My examples came from volcanic lava flows, not from sedimentary rock. I have never heard of a thunderegg being referred to as a septarian, prior to this conversation.

 

Regards.

Tony.

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If the structure has septa (partitions/walls), it is a septarian structure, hence the name.

 

I think the geological settings of Binh Thuan area are proper for the forming of septarian type nodules or concretions, considering that there is a tectonic fault zone with frequent mud erruptions. Maybe this document helps : Bui Van Thom, et al. 2016. Some study results of Cam Ranh - Binh Thuan mud eruption strip. Vietnam Journal of Earth Sciences Vol.38 (3) 256-276.

 

Some study results of Cam Ranh - Binh Thuan mud eruption strip.jpg

 

" Most of the mud eruption locations are distributed in a stretching strip, running in NE-SW direction from Cam Ranh - Ninh Thuan - Binh Thuan NE-SW tectonic fault zone and coinciding with a tectonically crushed zone. The erupted mud consists of sand, mud, clay. The clay contains alkaline montmorillonite, formed following chemical weathering and re-sedimentation processes from rocks containing alkaline minerals in a semi-arid climate area, located in a low terrain or a tectonic subsiding zone with a large fluctuation in groundwater level. The mud eruption has a close relation to factors (of) climate, topography, geomorphology, hydrogeology, , petrography and tectonic activities in the area. Among these, tectonic factors are the most important for they create not only soil and rock crushed zone, paving favorable conditions for strong weathering process at depth, but also to form canals to bring hot groundwater and minerals from certain depths upward, and by the effects of pressurized groundwater and partly due to the expansion in volume of bentonite clay pushing the muddy clay material through the tectonic cracks to the surface of the current terrain. The mud eruption process is not deep; but it may occur from a shallow level, about 4- 18 m below, under the impact of the above elements. "

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@abyssunder

Interesting read, but I see no mention of septarian in the paper. I did see mention of rhyolite lava underlying the area (along with other igneous rock).

The overhydrated system would not be conducive to a dried out (cracked) mud ball. I would classify this environment as a volcanic mud pot or hot springs, not as a sedimentary system. The clays and mud are derived from decomposing igneous rock.

 

I think You are using to broad of a definition for septarian. (In a geologic sense.)

The granite dome near My home has been fractured and the voids have been filled with quartz , this is a septarian by Your definition of a "septarian". As is a limestone cavern with calcite deposits inside.

 

If You google for septarian, septarian nodule or septarian concretion You will get a sedimentary structure 

If You google for thunderegg You will get a volcanic structure.

Although they look similar, there is no connection between them other than they are both mineral filled voids in rock.

 

The domed rind surrounded by the seams is a trait of a thunderegg not of a septarian (which has a flat rind surrounded by raised seams.).

The original post clearly shows a raised rind, hence - a thunderegg.

 

Tony

 

PS The only septarian pictured in this thread was the one that trisk posted, which clearly shows the flat rind with raised seams.

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On 12/24/2016 at 7:24 PM, ynot said:

PS The only septarian pictured in this thread was the one that trisk posted, which clearly shows the flat rind with raised seams.

 

Also, there is no metion of " thunder eggs".

 

I think, that is the only one (as type) documented and accepted worldwide as a status of septarian concretion of Moeraki Boulder, if that it is and I'm not wrong.

 

" Many concretions formed within mudstones contain large internal cracks, partly or completely filled with cements. These cracks give such concretions a 'septarian' structure, with the cement-filled cracks forming 'septa' cutting across the concretion. Recent studies of shale concretions have concentrated on their geochemistry rather than their textures.
The most important development has been the recognition of a sequence of diagenetic zones in marine shales, each zone defined by the dominant reaction contributing carbon dioxide to the pore-fluid (Curtis, 1977). The major features of carbonate-concretion chemistry, including their stable isotopes, can be related to the relative influences of oxidation, sulphate reduction, fermentation, and de-carboxylation zones during their formation (e.g. Raiswell, 1976; Irwin et al., 1977; Gautier & Claypool, 1984). However, the study and explanation of shale concretion textures, especially their most obvious common feature, septarian cracks, has received little detailed attention.
The current explanation for septarian cracks assumes an initially soft concretion interior, confined within a harder cemented shell, which subsequently dehydrates with the formation of shrinkage cracks (Crook, 1913; Richardson, 1919; Burt, 1932; Taylor, 1950; Lippman, 1955; Vanossi, 1964; Raiswell, 1971; Pettijohn, 1975). Opinions have differed on the nature of the precursor concretion interior that is capable of such shrinkage, between a clay-mineral-rich centre (Richardson, 1919; Raiswell, 1971) and a gel-like precursor (Lippman, 1955). The dehydration of clayey centres is attributed to chemical desiccation (Richardson, 1919, Raiswell, 1971). This explanation has two major drawbacks. First, the nature of any pre-cursor 'gel' is not clearly understood (Pettijohn, 1975) and, second, there are problems in explaining a suitable chemical environment during diagenesis capable of dehydrating clay-rich centres (Richardson, 1919). An early discussion of septarian cracks proposed an expansion mechanism of crack formation based on textural evidence incompatible with dehydration (Davies, 1913), although the mechanism of expansion was not understood.
This paper demonstrates that septarian cracks do not form by dehydration. It suggests that they are stress-induced fractures occurring during burial. Consideration of the conditions necessary for fracture provides potential constraints on the physical conditions of stress and fluid pressure present within the rock during burial. Crack-filling cements can be related to the diagenetic evolution of the whole concretion and used to date the fracturing relative to other events in the diagenetic history, thus potentially limiting the times when conditions appropriate for fracturing existed. " - excerpt form T. R. ASTIN. SEPTARIAN CRACK FORMATION IN CARBONATE CONCRETIONS FROM SHALES AND MUDSTONES. Clay Minerals (1986) 21, 617-631.

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On 12/28/2016 at 5:40 PM, abyssunder said:

Also, there is no metion of " thunder eggs".

Agreed, there is no mention of thundereggs in the paper You linked, but there is mention of rhyolitic lavas (the parent rock of thundereggs) underlying the mud volcanos. There is also mention of "other" igneous rock, but nothing mentioned about sedimentary rock, in the area.

I have never heard of septarians being found in volcanic mud pots or hot springs.

 

The other papers You have cited talk about sedimentary formations being the type of rock that septarians are created from/in.

I agree that septarians are sedimentary, but the rocks in question (and the ones I posted) are not sedimentary rock, they are igneous rocks

I dug mine out of decomposed rhyolitic lava flows.

 

You are looking at a persimmon and calling it an orange.

 

Again I say a thunder egg is volcanic rock and a septarian is sedimentary rock. They do not look the same. They are not the same.

The original object in this thread is a volcanic thunder egg - not a sedimentary septarian concretion.

 

Respectfully Yours,

Tony

 

 

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