EXPERIMENTS REGARDING THE SPREAD OF "PYRITE DISEASE" IN MUSEUM COLLECTIONS

Museum specimens that contain pyrite are subjected to destruction over time due to the growth of hydrous sulfate minerals in the cracks. Oxidation and hydrolysis of pyrite eventually results in sulfuric acid, also a culprit in acid mine drainage. A puzzling problem is that "pyrite disease" seems to spread to previously unaffected specimens in storage cabinets. One hypothesis is that efflorescent minerals dry during seasons of low humidity and can spread to other specimens by airborne transport.

To test this hypothesis, efflorescent minerals from one pyrite disease specimen were dried in a vacuum oven at 120°C, along with the clays and quartz found in the matrix. These were then added to polished sections of pyrite as seeds. Humidity was buffered with two different saturated salt solutions, NaCl (75% R.H.)and NaBr (56% R.H.). Each container included the pyrite with the dehydrated powder and also a control specimen, beginning in June of 2008. In the summer of 2012 the specimens were analyzed with reflectance Fourier Transform Infrared (FTIR) spectroscopy and reflected light microscopy.

At both humidities, sections with seeded sulfate minerals were significant more oxidized than the controls, which supports the initial hypothesis. Petrography showed well-developed crystals of halotrichite spreading on the NaCl-buffered pyrite but very few new crystals were found on the NaBr-buffered slide. Minerals identified by FTIR at 56% R.H. include halotrichite, alunogen, jarosite, melanterite ±coquimbite ±copiapite. At 75% R.H., FTIR showed the presence of halotrichite, melanterite, jarosite, copiapite, szomolnokite ±coquimbite.

Efflorescent minerals readily grow in a new environment and enhance the oxidation that occurs, even at 56% R.H. Treatments for pyrite disease should involve both quarantine of affected specimens and strict control of relative humidity.

FTIR spectroscopy in this work was supported by National Science Foundation grant EAR-0929898 to RCT.