Can Anyone Explain Why Mother Of Pearl Stays On Some Fossils Please?

[fossilized6s]

I've found some awesome pieces with the mother of pearl still coating the shells, why is this? Is it more of a petrification process and the pearl is just hard enough to stick around?

Here's just a few examples. I have plenty more.

[Missourian]

The iridescence-causing layered microstructure of the shell was preserved. Most of the time, the fine structure is destroyed by recrystallization.

[painshill]

Nacre consists of rounded or polygonal (normally hexagonal) tablets of aragonite, which is a form of calcium carbonate. The plate-like tablets are arranged in broadly continuous, regular, mutually parallel laminae which are separated by sheets of organic matrix. That matrix is composed of biopolymers such as chitin, lustrin and silk-like proteins.

It’s that unique arrangement, coupled with the fact that the thickness of the aragonite tablets approximates to the wavelength of visible light, which creates the interference pattern of iridescence we call “mother of pearl”.

The other parts of mollusc shells are composed principally of aragonite, with some calcite. Although they’re both calcium carbonates, aragonite is geochemically unstable over long periods of time and readily converts to stable calcite in most shelly fossils by recrystallization during diagenesis and post-diagenetic alteration. Those processes also destroy the organic components of the nacre.

Although it’s possible for the tablet arrangement of the original nacreous structure to be preserved (it’s sometimes replaced as a pseudomorph by the phosphate mineral apatite), the iridescence doesn’t survive in those circumstances. Intact original nacreous structures with iridescence are only seen in two sets of circumstances. Young fossils, or those where something has prevented the recrystallization… and that “something” is most usually petroleum or one of its derivatives.

Famously, for example, the Buckhorn Lagerstätte of Oklahoma is rich in aragonitic shelly fossils preserved with their original iridescent nacre. In fact it’s the oldest deposit in the world which contains such material. It’s a late Middle Pennsylvanian palaeo-seafloor oil seep deposit which became impregnated with asphalt before the sediments lithified and that prevented the nacre from recrystallizing.

Edited March 4, 2014 by painshill

[fossilized6s]

Thank you guys!

[cowsharks]

Wow. I had to re-read each paragraph in order to take it all in. A very impressive, succint, and understandable explanation.

Daryl.

[Missourian]

Famously, for example, the Buckhorn Lagerstätte of Oklahoma is rich in aragonitic shelly fossils preserved with their original iridescent nacre. In fact it’s the oldest deposit in the world which contains such material. It’s a late Middle Pennsylvanian palaeo-seafloor oil seep deposit which became impregnated with asphalt before the sediments lithified and that prevented the nacre from recrystallizing.

I'm not sure if this is true 'mother of pearl' (or even part of a shell, to be honest):

But if it is, it is nearly as old as the Buckhorn deposit. It is in a phosphatic concretion from the Muncie Creek Shale, Missourian Stage, Upper Pennsylvanian.

Edit: the fragment is just a few mm across.

Edited March 6, 2014 by Missourian

[painshill]

I'm not sure if this is true 'mother of pearl' (or even part of a shell, to be honest):

But if it is, it is nearly as old as the Buckhorn deposit. It is in a phosphatic concretion from the Muncie Creek Shale, Missourian Stage, Upper Pennsylvanian.

Edit: the fragment is just a few mm across.

I don't see why it couldn't be preserved nacre. The Iola Formation, of which the Muncie Creek Shale is part, is oil-bearing is it not? The Avant Limstone in particular - which sits above the Muncie Creek Shale in Oklahoma - is a geological petroleum reservoir. There's a lot of oil-staining in rocks throughout the series and those are the kinds of conditions that help prevent the recrystallisation that destroys nacre.

[Missourian]

I don't see why it couldn't be preserved nacre. The Iola Formation, of which the Muncie Creek Shale is part, is oil-bearing is it not? The Avant Limstone in particular - which sits above the Muncie Creek Shale in Oklahoma - is a geological petroleum reservoir. There's a lot of oil-staining in rocks throughout the series and those are the kinds of conditions that help prevent the recrystallisation that destroys nacre.

Although these beds seem to be free of petroleum, we occasionally do find tar-filled brachiopods, including in the overlying Argentine Limestone.

[Bullsnake]

Although these beds seem to be free of petroleum, we occasionally do find tar-filled brachiopods, including in the overlying Argentine Limestone.

I'm going to guess you know this, Mitch. But there are oil wells in western Ks. pumping from Penn. strata, and I believe more specifically the Kansas City group.

Your tar/oil filled brachiopods immediately came to mind when I read that.

Also, I don't know if this may have any bearing on what painshill stated in relation to your specimen above.

Edited March 6, 2014 by Bullsnake

[painshill]

I'm going to guess you know this, Mitch. But there are oil wells in western Ks. pumping from Penn. strata, and I believe more specifically the Kansas City group.

Your tar/oil filled brachiopods immediately came to mind when I read that.

Also, I don't know if this may have any bearing on what painshill stated in relation to your specimen above.

Highly relevant, I would think.

[Missourian]

I'm going to guess you know this, Mitch. But there are oil wells in western Ks. pumping from Penn. strata, and I believe more specifically the Kansas City group.

Your tar/oil filled brachiopods immediately came to mind when I read that.

Also, I don't know if this may have any bearing on what painshill stated in relation to your specimen above.

I was wondering about the source level of the eastern Kansas wells as well as those out west, and then I found this:

http://www.kgs.ku.edu/Publications/Bulletins/Sub9/page2.html

Desmoinesian Stage:

Missourian Stage:

I love the KGS.

[Herb]

Nacre consists of rounded or polygonal (normally hexagonal) tablets of aragonite, which is a form of calcium carbonate. The plate-like tablets are arranged in broadly continuous, regular, mutually parallel laminae which are separated by sheets of organic matrix. That matrix is composed of biopolymers such as chitin, lustrin and silk-like proteins.

It’s that unique arrangement, coupled with the fact that the thickness of the aragonite tablets approximates to the wavelength of visible light, which creates the interference pattern of iridescence we call “mother of pearl”.

The other parts of mollusc shells are composed principally of aragonite, with some calcite. Although they’re both calcium carbonates, aragonite is geochemically unstable over long periods of time and readily converts to stable calcite in most shelly fossils by recrystallization during diagenesis and post-diagenetic alteration. Those processes also destroy the organic components of the nacre.

Although it’s possible for the tablet arrangement of the original nacreous structure to be preserved (it’s sometimes replaced as a pseudomorph by the phosphate mineral apatite), the iridescence doesn’t survive in those circumstances. Intact original nacreous structures with iridescence are only seen in two sets of circumstances. Young fossils, or those where something has prevented the recrystallization… and that “something” is most usually petroleum or one of its derivatives.

Famously, for example, the Buckhorn Lagerstätte of Oklahoma is rich in aragonitic shelly fossils preserved with their original iridescent nacre. In fact it’s the oldest deposit in the world which contains such material. It’s a late Middle Pennsylvanian palaeo-seafloor oil seep deposit which became impregnated with asphalt before the sediments lithified and that prevented the nacre from recrystallizing.

WOW!

[Tennessees Pride]

I've found some awesome pieces with the mother of pearl still coating the shells, why is this? Is it more of a petrification process and the pearl is just hard enough to stick around?

Here's just a few examples. I have plenty more.

2014-03-03_16-54-15_489.jpg

2014-03-03_16-58-03_289.jpg

Oh yes!...you have some very fine examples there Charlie! That's exactly what the outside of that round Ammonite from Coon Creek Science Center had on it.

[Tennessees Pride]

I'm not sure if this is true 'mother of pearl' (or even part of a shell, to be honest):

post-6808-0-85298700-1368516868.jpg

But if it is, it is nearly as old as the Buckhorn deposit. It is in a phosphatic concretion from the Muncie Creek Shale, Missourian Stage, Upper Pennsylvanian.

Edit: the fragment is just a few mm across.

Sir, in my unprofessional opinion, it looks like you may have ran up on a thin layer of hydrated silica=Opal. Opal has been known to replace Calcite @ times also. (Shells) Edited April 22, 2014 by Tennessees Pride