A review of “pyrite disease” for paleontologists, with potential focused interventions

Abstract

A literature review of the chemical reactions involved in pyrite oxidation/hydration ("pyrite disease") in geological or fossil collections gives direction to a suite of focused interventions. Reactions on the pyrite surface lie at the heart of the chemical process, accompanied by the movement of electrons on and through the pyrite semiconductor. Control of these electrons ultimately may be futile, but examination of the reactions at the atomic level leads to new possibilities for treatment, and identifies why some treatments are ineffective. This review also identifies gaps in our understanding of the oxidation and hydration reactions. Fossil biomaterials-bone or shell-often contain or are partially replaced by pyrite. Acidity produced by pyrite decay destroys these materials. Older treatments focus on acid neutralization, and humidity control as solutions for megascopic problems. Focused interventions target specific steps in the chemical reactions at the atomic scale. Interventions are informed by identification of all the minerals participating in the process, and accurate characterization of the bone, pyrite and sedimentary matrix. Bone minerals and pyrite are structurally and chemically heterogeneous, so each intervention requires bench testing, complimented by analytical measurements. Chemically passivating the unreacted pyrite surface shows the greatest promise. Anticipation of a new specimen's susceptibility to decay is key. Decay may be accelerated using techniques of humidity buffering with saturated salt solutions. Conductivity of pyrite (which varies over four orders of magnitude) may be measured. A database of pyrite conductivity is highly desirable.

When Abnormality Becomes Perennial in a Reduced Population: The Case of Altudostephanus longicostis gen. et sp. nov. (Valanginian Ammonites, South-Eastern France)

“…As the studied fossils are preserved in the form of 'pyritic' s.l. nuclei ('iron sulphidecontaining', following Rouchon et al, 2011 [11]), they are likely to deteriorate over time more or less quickly because of the chemical reactions involved in pyrite oxidation/hydration (Larkin, 2011 [12]; Tacker, 2020 [13]).…”