Is this pyrite disease?

[JUAN EMMANUEL]

Hi guys I recently found this nice sized Pholadomorpha pholadoformis at the Humber River in Etobicoke, Ontario. It belongs to the Georgian Bay formation and is late Ordovician in age. The specimen has pyrite in addition to the black film. Does this fossil have some sort of pyrite disease to it?

[JUAN EMMANUEL]

[facehugger]

I don't think so. Pyrite disease that i have encountered (i live in Houston which has legendary humidity all year round) the pyrite forms a sort of dust on it - it's not black, it's usually orange or white. sometimes I like to store pyrite fossils with some silica beads, but in houston, it just prolongs the inevitable...

[JUAN EMMANUEL]

3 minutes ago, facehugger said:

I don't think so. Pyrite disease that i have encountered (i live in Houston which has legendary humidity all year round) the pyrite forms a sort of dust on it - it's not black, it's usually orange or white. sometimes I like to store pyrite fossils with some silica beads, but in houston, it just prolongs the inevitable...

I also found this fossil near the water too.

[jpc]

I don't think so either... I agree that pyrite disease is seen as a powdery white deposit (wrong word) on the fossil. 

[Coco]

I have read a lot about pyrite disease on this forum, and I share (finally) my opinion.

Pyritized ammonites from some sites will be perfectly preserved for decades, while others from other sites will turn into powder in the longer or shorter term.

 

I noticed one thing : when a pyritized ammonite (which applies to the other fossils, but I’m talking about my experience) breaks down, it smells very strongly of sulfur. I think that when the marly soil is very rich in sulphur (you can feel it in the air, but also on your hands) the fossils do not keep. However, pyritized fossils from some other marl sites will not move for 20, 30 or 40 years.

 

For me, pyrite disease occurs mainly when the % of sulphur is high in pyrite, formula FeS2. My ammonites from an old site in Deux-Sèvres (France) never moved, while others from elsewhere may have deteriorated.

 

Coco

[Ludwigia]

Looks ok to me. As far as I understand it, the powdery white deposit is a form of gypsum CaSO4.2H²O, calcium+sulphur and water, which occurs when water gets into the crystal lattice, so it depends on the stability of that lattice whether it's affected.

[Mark Kmiecik]

As I read this thread I begin to believe that some folks are misunderstanding "pyrite disease". It is not pyrite attacking a fossil specimen, but a specimen that is composed of a large percentage of pyrite literally turning into powder (extreme case scenario) as the iron sulfide reacts with the environment and changes composition. It is the pyrite itself that is the victim of the "disease", which may destroy any specimen with a great degree of pyratization.

 

Pyrite Oxidation: Review and Prevention Practices Shinya, A. and L. Bergwall The Field Museum, Chicago IL

 

Pyrite (FeS2 ) is a common mineral found in sedimentary rock and fossils, and its decay is a major problem in the conservation of fossil specimens. Pyrite oxidation, also referred to as pyrite disease or pyrite decay, is identified by a sulphuric acid odor, white crystalline powder, yellow sulphide powder, and/or gray to yellowish microcrystalline mass in and out of specimens. Its presence can be devastating to a geological collection. In the presence of oxygen, pyrite breaks down to ferros sulphate (FeSO4 ) and sulphur dioxide (SO2 ). If water is present, sulphuric acid (H2 SO4 ) is also produced and can cause damage to labeling and storage containers. The most effective method to preventing rapid pyrite oxidation decay is to store specimens within a moisture and oxygen barrier containing an oxygen scavenger. Further oxidation can be reduced or eliminated by storing specimens in an environment with a humidity level below 30%. Ammonium gas and ethanolamine thioglycollate treatments neutralize sulphuric acid and remove ferros sulphate, and are reportedly effective in partly or completely removing oxidation reaction products. Specimens that contain large amounts of pyrite and are in danger of losing morphological information through pyrite oxidation should be molded and cast. Because latex rubber contains ammonium, its use as a molding material can have the added benefit of neutralizing sulphuric acid and ferros sulphate. Although not tested in a controlled scientific experiment, it has been reported that this method was successful in halting the oxidation process in some specimens.

 

More info here: http://vertpaleo.org/Education-Resources/Preparators-Resources-PDF-files/Pyrite-Oxidation_Shinya_and_Bergwall_2007.aspx#:~:text=Pyrite oxidation%2C also referred to,devastating to a geological collection.