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Identity HelpSeptarian Nodule (Septurian)

18th Aug 2006 00:52 UTCMoonCave

Septarian Nodule (sand concretion of a mud ball where yellow calcite crystallized in the cracks. These can be narrow and minuscule at first and then open into larger cavities. Found in Utah)is obviously not the correct mineral name for this specimen.

What exactly would be an acceptable and accurate name ???


18th Aug 2006 01:40 UTCJeremy Zolan

well, in terms of mineral species, that would be calcite. I would just label it as a Septarian Nodule as this is acceptable (at least to me and most collectors) but it could also be labeled as Calcite var. Septarian Nodule.


18th Aug 2006 02:51 UTCKarl Volkman Expert

Actually i wouldn't label it as "calcite var septurian nodule". The reason is because the calcite is only one of the minerals that is present in most S.N. The darker brown rims on many of the nodules have turned out to be aragonite so you have at least to minerals present.

Then you have the matrix itself. These nodules are actually pseudofossils (think "fossilized" ripple marks, raindrop hits, etc...) in this case what you have are "fossilized" mud cracks. These formed when the lake bed where these were formed dried out. As the mud of the lake bottom dried it contracted and voids formed. The lake bed was subsequently covered with new lake and the older one was buried. The water from the new lake seeped down through the sedimentary rock of the old lake and picked up trace amounts of calcium in passing. when the water entered the voids it would pool and the calcium would deposit out as aragonite and calcite.

After all the long winded explanation it comes down to what you have is properly called a Septurian nodule


18th Aug 2006 03:52 UTCAlan Plante

As Karl notes, septarian nodules are pseudo-fossils - not minerals, *per se*. Technically they are rocks. The name "septarian nodule" is the accepted name for them and should be used on labels; but it should be clear that what you are labeling is a rock, not a mineral. - Nothing wrong with that. - Alan

18th Aug 2006 05:32 UTCChris Tucker Expert

Your specimen would be calcite in a septarian nodule.

A septarian nodule is a kind of rock, it is not a variety of a mineral and can not be described as such. A septarian nodule is a kind of concretion, not all concretions contain separations, or open spaces caused by a variety of factors. These open spaces are often attributed to drying, shrinkage and compression.

Concretions do not form from the seasonal drying of a lake bed as Karl mentioned. They are formed shortly after deposition of the surrounding sediment. Mineral rich fluids flowing through the sediment deposit minerals around a nucleus of some sort. This nucleus could be a could be just about anything, including organic matter. If you have had plenty to drink and are crossed eyed, you could use the term "pseudo fossil" to describe a concretion.



18th Aug 2006 06:44 UTCKarl Volkman Expert

I respecfully disagree that septerian nodules are concretions. As you pointed out in the definition of concretions "Mineral rich fluids flowing through the sediment deposit minerals around a nucleus of some sort". Visual observation alon disproves the idea that speteria are concretions. The clay/calcite/aragonite relations tat are displayed in them could not be formed as a concretion. The sequence for the formation of a Septerian Nodule is as follows:

1. lake dries out

2. Mud in the lake sediments dries and hardens with voids forming due to shrinkage of the clay

3. fluids flow through sedimentary rock that was the lakebed and pools in the voids.

4. Aragonite is deposited around the edges of the void

4. Calcite iss deposited on the aragonite

if these were concretions then the centers would be solid mineralization with successive layering outward. This is not present in Septerian as evidenced by the numerous hollow nodules that have been found.


18th Aug 2006 07:04 UTCKarl Volkman Expert

oopps Forgot one thing.

In regard to my classifying these as pseudofossils i have done so because the definition of tracefossil specificly defines them as traces of prehistoric oranizums thus excluding Septerian Nodules, raindrops, ripplemarks, etc...


18th Aug 2006 07:55 UTCChris Tucker Expert


Sorry, but you are wrong. Septarians are kinds of concretions, that is a fact. It is well proven and there is no arguing it.

The depositional sequence of minerals in a septarian is essentially meaningless; from locality to locality differences will be encountered. Many are found without any additional mineral inside. Numerous other minerals are also commonly present. Besides the already mentioned calcite and aragonite other minerals are commonly found in septarians including barite, quartz, pyrite and marcasite along with their alteration products, whewellite, analcime, gypsum, and many more.

Following are a few references to the subject. If you would like more, I would be happy to come up with a few others.



Astin, T.R. 1986. Septarian crack formation in carbonate concretions from shales and mudstones.Clay Minerals. 21:617-632.

Astin, T.R. and I.C. Scotchman. 1988. The diagenetic history of some septarian concretions from the Kimmeridge Clay, England. Sedimentology. 35:349-368.

Bassler, R.L. 1936. Concretions-freaks in stone.Smithsonian Report for 1935. p.321-326 (and 3 plates).

Bates, R.L. 1938. Occurrence and origin of certain limonite concretions. Journal of Sedimentary Petrology. 8:91-99.

Berner, R.A. 1968. Calcium Carbonate concretions formed by the decomposition of organic matter.Science. 159:195-197.

Campbell, T.J. and W.L. Roberts. 1986. Whewellite from South Dakota and a review of other North American localities.Mineralogical Record. 17:131-133.

Campbell, T.J. et al. 1987. Famous mineral localities: Elk Creek, South Dakota. Mineralogical Record. 18:125-130.

Carlson, E.H. 1977. Mineralogy of the septarian concretions from Anonymous.Crystal growth and habit. United States:Mineralogical Society of America (3rd Mineralotical Society of America-Friends of Mineralogy Symposium -- Tucson, AR, Feb.13-14, 1977.p???

Clifton, H.E. 1957. The carbonate concretions of the Ohio Shale. Ohio Journal of Science, 57(2):114-129.

Crook, T. 1913. Septaria: a defense of the "shrinkage" view. Geologcial Magazine. 10:514-515.

Davies, A.M. 1913. The origin of septarian structure. Geological Magazine. 10:99-101.

Desrochers, A. and I.S. Al-Aasm. 1993. The formation of septarian concretions in Queen Charlotte Islands, B.C.: evidence for microbially and hydrothermally mediated reactions at shallow burial depth.Journal of Sedimentary Petrology. 63:282-294.

Duck, R.W. 1995. Subaqueous shrinkage cracks and early sediment fabrics preserved in Pleistocene calcareous concretions.Journal of the Geological Society of London. 152:151-156.

England, B.M. 1988. A calcite-strontianite-celestine-magnesian calcite association in septarian siderite te concretions from Late Permian sediments at Liddell, Hunter Valley, N.S.W.Australian Mineralogist.3:19-23.

Hyde, C. and R.A. Landy. 1966. Whewellite from septarian concretions near Milan, Ohio.American Mineralogist. 51:228-229.

Kennedy, M. 1964. Something about septaria.Lapidary Journal. 18:102-105.

Lindholm, R.C. 1974. Fabric and chemistry of pore filling calcite in septarian veins: models for limestone cementation.Journal of Sedimentary Petrology. 44:428-440.40.

MacDonald, R.H. and C.W. Byers. 1981. A sequence of distinct concretion horizons in the shaly facies of the Greenhorn Formation, northwestern Black Hills. Geological Society of America, Abstracts with Programs 13(#6):287.

Malicse, A., B. Johnson and J. Mazzullo. 1994. Depositional environments of the Tidwell Member of the Morrison Formation: Cache Valley, Utah. Geological Society of American, Abstracts with Programs.26(n.7):494.

Millen, T.M. 1983. Stratigraphy and petrography of the Green River Formation, Gunnison Plateau, central Utah.Geological Society of America, Abstracts with Programs. 15(#4):265.

Mozley, P.S. 1996. The internal structure of carbonate concretions in mudrocks: a critical evaluation of the conventional concentric model of concretion growth.Sedimentary Geology.103:85-91.

Pecora, W.T. and J.H. Kerr. 1954. Whewellite from a septarian limestone concretion in marince shale near Havre, Montana.American Mineralogist.39:208-214.

Richardson, W.A. 1919. On the origin of septarian structure. Mineralogical Magazine. 18:327-338.

Savrda, C.E. and D.J. Bottjer. 1988. Limestone concretion growth documented by trace-fossil relations. Geology. 16:908-911.

Spendlove, E. 1992. Septarian nodules. Rock & Gem. 22:52-54,71,76-77.

Tandon, S.K and P.F. Friend. 1989. Near-surface shrinkage and carbonate replacement processes, Arran Cornstone Formation, Scotland. sedimentology.36:1113-1126.

Tarr, W.A. 1921. Syngenetic origin of concretions in shale.Geological Society of America, Bulletin. 32:373-384.

Todd, J.E. 1913. More about septarian structure. Geological Magazine. 10:361-364.

Weeks, L.G. 1953. Environment, mode of origin and facies relationships of carbonate concretions in shale.Journal of Sedimentary Petrology, 23:162-173.

18th Aug 2006 16:47 UTCKarl Volkman Expert

Are any of these available for download online?

18th Aug 2006 20:07 UTCChris Tucker Expert


I'm not aware of any of the titles on line, but I assume that some are. Any decent library should have some of the titles.

However, this is on line.



24th Aug 2006 02:29 UTCMichael Hatskel


Septarians are in fact concretions. And sometimes they may contain trapped fossils as a center.

The depositional sequence you presented lacks an explanation of why it is a NODULE. If it were just a piece of crack network on the ground, no rounded nodule would form.

If I remember it right, the name "Septarian" comes from the fact that rounded nodule cracking creates SEVEN rays of crack.

Good luck with the list of references!


11th Sep 2006 20:22 UTCMargaret

Wow, I'm just a hayseed from North Dakota, reading about a pair of bookends I bought at a rock and gem show. I never dreamed their origin would be so complicated and could generate so much debate! Carry on gentlemen....

16th Sep 2006 19:49 UTCCharlenne

Wow, I'm with Margaret...who knew there was so much information and debate.

I'm from the South and just vacationed in Wyoming. I bought a small carving and was told it was Septarian Nodule. Having never heard of that I "Googled" it and found the answer.

For Karl, who would like an online reference, here's a link I found from the Australian Government

16th Sep 2006 19:53 UTCCharl

Not sure why this link didn't post before.

16th Sep 2006 20:57 UTCAnonymous User


Thank you for that great explanation. Dr. Moyle from Utah State Univ. has been researching these for decades and you pretty much summarized his entire life's work.

I have read most of his papers, if not all, and he also used an explanation of decaying organic matter (algae or something like it) to explain the hollow cavities.

I am not sure he has ever published that thought but he does us it in his lectures.

I have from Utah hundreds (maybe thousands) of these I have cut and polished and often I find that clam and snail shells and ammonites have been the center for nucleation.

I have also found them with amethyst coating barite crystals up to 3 inches long, pyrite (marcasite) coating barite, and yellow calcite crystals up to 3 inches.

The brown ring around the calcite is sometimes siderite and not aragonite, I believe.


18th Sep 2006 06:55 UTCcanadaman

has anyone ever found Sepatarian nodules in Canada?

13th Feb 2011 02:52 UTCSam Shale

Hi there folks, just to boast other than the New Zealand Museum i have to say that i have the largest collection of septarian Nodule known to Man. and they are Gigantic and Beautiful. Sam Australia.

13th Feb 2011 03:02 UTCSam Shale

Sam Shale Wrote:


Hi there folks, Just to boast other than the New Zealand Museum i have to say that i have the largest collection of Septarian Nodule known to

Man, And they are Gigantic and Beautiful.Sam, Australia. They are Similar but most Spectacular than any other Nodule Ihave ever seen.

13th Feb 2011 12:49 UTCDavid Von Bargen Manager

"has anyone ever found Sepatarian nodules in Canada? "

The Formation of Septarian Concretions in Queen Charlotte Islands, B.C.: Evidence for Microbially and Hydrothermally Mediated Reactions at Shallow Burial Depth

Andre Desrochers, Ihsan S. Al-Aasm

Journal of Sedimentary Research

Volume 63 (1993)

13th Feb 2011 14:48 UTCsam shale

hi there David i have never found any there, but there are some currently on sale at ebay. from canada at the moment.

14th Feb 2011 08:13 UTCRock Currier Expert

It seems that a great deal of what we talk about with each other can be boiled down to "mines bigger/better than yours".

23rd Jul 2011 04:03 UTCMitch

We have over 100 the size of footballs.. (advertisement deleted) Rock Currier, moderator

23rd Jul 2011 04:41 UTCStephanie Martin

hmm.... those look an aweful lot like the ones from Morocco. Are you digging them up in Alberta?

8th Jan 2016 06:09 UTCPete

Septarian comes from the Latin Septa meaning a separation. Seven in Latin is Septem.

Septarian nodules do occasionally have seven separations but more often have a lesser or greater number.

8th Jan 2016 22:44 UTCGary Weinstein


A little history on the formation;

Septaria, concretions and fossils such as the ferns etc. from Mazon Creek, Ill. formed around an object (shell, leaf, animal, etc.) by rolling back and forth in a shallow (large) lake environ, with the tide, building up layers of sticky mud which dried out when the lake receded during the dry season (summer). This transpired over millennia and it is difficult for our brains to comprehend it. Sometimes you can see the layers from the many seasons of forming. I often find Turritella shells in Utah Septarians just like the Wyoming agatized shells. They were later buried in sediments and the cracks were filled in through seepage. In Pennsylvania there are concretions the size of a car. When you know how things form it is much easier to understand formations and explain to others. If the ocean was not sand at the shore, but mud, just think of all the concretions we would have. That is, I trust some of you have seen a shell rocking back and forth in the surf like Florida or Islands somewhere.

Hope this helps,


24th Oct 2016 17:11 UTCDave Crosby

Septarian nodules are found around the world from many time periods, but there are apparently certain requirements for their formation. Water, bentonite mud, calcium bearing life forms, shakeup and grouped burial by harmonic earthquake vibrations followed by internal expansion cracking caused by decomposition gas. How else do they explain the hollow centers? Cracking happened more than once.

I have personally collected septarians from the Cretaceous Frontier Fm (~90Ma) between Mt. Carmel and Orderville Utah. I find that lots of the "cracks" are actually shells and bits of shells.

I believe body oils seeped into the surrounding mud, making their clumps more cohesive and durable than the surrounding mud.

Some calcite from bones and shells dissolved and re-precipitated several times.

1st precipitation is next to the mud.

2nd precipitation is darker, containing iron as siderite.

3rd and later are much lighter in color, obviously formed in a void.

Image from WEB.

From Wikipedia:

"Septarian nodules, are concretions containing angular cavities or cracks, called "septaria". The word comes from the Latin word septum; "partition", and refers to the cracks/separations in this kind of rock.[2]

There is an incorrect explanation that it comes from the Latin word for "seven", septem,[3] referring to the number of cracks that commonly occur."


by T. R. ASTIN pp 617-618

"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.


This section summarizes the common features of septarian concretions that need to be explained by any realistic mechanism of formation. Chemical information comes from the literature and textural information from concretions examined from Jurassic (Lias, Oxford, Ampthill and Kimmeridge Clays) and Eocene (London Clay) shale formations in England, and from literature descriptions.

(1) Septarian cracks are found within concretions which have been shown to form by progressive outward cementation (Raiswell, 1971). This is demonstrated by

(a) decreasing proportions of cement relative to sedimentary grains towards concretion margins (Vanossi, 1964; Raiswell, 1971),

(b) the pattern of laminations passing through concretions and host shales showing more compaction in the marginal parts of concretions (Oertel & Curtis, 1972), and

(c) systematically changing chemistry (both in the elements present and in the stable isotopic proportions present) from the centres to the margins, which indicates outward concretion growth through several depth-related diagenetic zones (Raiswell, 1976; Irwin et al., 1977; Hudson, 1978; Gautier & Claypool, 1984).

(2) Investigations of the stable isotopic composition of carbon and oxygen (Hudson, 1978; Coleman & Raiswell, 1981; Marshall, 1983) and trace-element composition (Boles et al., 1985) of the earliest crack-filling cements show that these were deposited while the cements of the outermost parts of the concretion were forming. Thus fracturing started in the later stages of concretion growth. Carbon isotopic values of the septarian cements in Jurassic concretions suggests formation within a diagenetic zone dominated by fermentation reactions, with some contribution from sulphate reduction (Hudson, 1978; Marshall, 1983).

(3) Septarian cracks are widest in concretion centres, narrowing towards concretion margins, and rarely reach the concretion surfaces (Figs 1,2,3).

(4) Within simple sub-spherical concretions, cracks consistently show the same pattern of preferred orientation. Horizontal sections through concretions show polygonal pattern of cracks with no preferred orientation (Figs ld, 2a,b), while vertical sections show dominantly vertical cracks (Figs la,b,c, 2b). Cracks may become sub-parallel, and close to the concretion margins (Figs la, c, 2b). More irregular and complicated crack patterns occur in irregular shaped concretions.

(5) Some concretions show two generations of cracks clearly separated in time, with the later cracks cross-cutting earlier ones (Figs 2a, 3). "

27th Oct 2016 21:04 UTCRobert Verish

Hi there folks,

Just wanted to thank Mindat for hosting this thread, and to everyone who contributed.

I realize that this is an old thread, but it appeared high-up in the results when I Google-searched the term "Septarian nodule". I think that it is important to note that, as of my writing this (2016), there still is no commonly accepted explanation for how the cracks (septaria) formed in these "concretions".

Here is the current conventional wisdom, according to Wikipedia:

"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)."
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