Nanoscale structure and compositional analysis of manganese oxide coatings on the Smithsonian Castle, Washington, DC

Sharps, Meredith C.; Grissom, Carol A.; Vicenzi, Edward P.

doi:10.1016/j.chemgeo.2020.119486

Cited by 5 publications

(13 citation statements)

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“…The hypothesis of an external source of Mn was dismissed both because no external source could be identified and because such an external source would have resulted in a more homogeneous or azimuthally oriented distribution of areas exhibiting patinas. Furthermore, the possible aerial deposition of Mn originating from automotive traffic would most likely be associated with a significant enrichment in other "traffic-related" elements such as Ba, Zn, or Pb (Macholdt et al, 2017;Ortiz-Montalvo et al, 2018;Sharps et al, 2020), and that was not detected. In addition, the contribution of such an external "traffic-related" source of Mn is expected to be minor in the center of a small town (∼ 18 000 inhabitants as of 2018) with cobbled streets.…”

Section: Discussionmentioning

confidence: 99%

“…Compared to the bulks, surface compositions exhibit lower SiO 2 contents (Table 1), most probably as the result of dilution effects. Irrespective of the presence of patina, surfaces are enriched in S and Ca compared to bulk compositions (Table 1), possibly as the result of sulfate (gypsum) precipitation, frequent on building stones (Schaffer, 1932;Siegesmund et al, 2002;Thomachot, 2002;Gaviño et al, 2005;Marszalek et al, 2014). The surface of L1 does not exhibit such S enrichment, however.…”

Section: Sample Characterizationmentioning

confidence: 96%

“…Similar-looking thin black layers were previously observed on monuments built from granite or sandstone. These dark layers most often consist of Fe-(oxihydr)oxides (Nord and Ericsson, 1993;Thomachot and Jeannette, 2004;Mertz, 2010) and/or Mn-(oxihydr)oxides (Vicenzi et al, 2016;Sharps et al, 2020), but their precise mineralogical composition and their formation mechanisms often remain elusive. There are only a few studies on the appearance and origin of such dark layers on architectural stones (Nord and Ericsson, 1993;Vicenzi et al, 2016;Sharps et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

“…These dark layers most often consist of Fe-(oxihydr)oxides (Nord and Ericsson, 1993;Thomachot and Jeannette, 2004;Mertz, 2010) and/or Mn-(oxihydr)oxides (Vicenzi et al, 2016;Sharps et al, 2020), but their precise mineralogical composition and their formation mechanisms often remain elusive. There are only a few studies on the appearance and origin of such dark layers on architectural stones (Nord and Ericsson, 1993;Vicenzi et al, 2016;Sharps et al, 2020). One hypothesis is that Fe and/or Mn comes from the underlying rock, being solubilized by rainwater; subsequently, Fe and/or Mn migrates and precipitates onto the surface rock (Nord and Ericsson, 1993).…”

Section: Introductionmentioning

confidence: 99%

“…One hypothesis is that Fe and/or Mn comes from the underlying rock, being solubilized by rainwater; subsequently, Fe and/or Mn migrates and precipitates onto the surface rock (Nord and Ericsson, 1993). Alternatively, aeolian deposition has also been proposed as a possible source for Mn and associated elements (e.g., Ba, Pb, Zn) that compose the black layer on the Smithsonian Castle (Washington, DC; Sharps et al, 2020) or on the Freiburger Münster (Freiburg, Germany; Macholdt et al, 2017). Dark layers on sandstone surfaces found in natural environments (rock/desert varnish) are mainly composed of clay minerals and poorly crystallized Fe-and Mn-(oxihydr)oxides (Engel and Sharp, 1958;Potter and Rossman, 1979;Krumbein and Jens, 1981;McKeown and Post, 2001;Dorn, 2007;Garvie et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

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Characterization and origin of the Mn-rich patinas formed on Lunéville château sandstones

et al. 2021

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Abstract. The formation of iron- and/or manganese-rich dark patinas on sandstones is a common natural phenomenon that occurs also on building stones. Lunéville château, in eastern France, presents such patinas that developed either under natural conditions (rain and time) or after an accidental fire and exposure to significant amounts of water as part of attempts to extinguish the fire. The present study aimed at characterizing both types of patinas in an effort to determine their formation mechanisms and Mn sources. In both cases, Mn required for patina formation likely derives from the reductive dissolution of Mn-rich minerals present in pristine sandstones, as suggested by the contrasting mineralogy and chemistry of Mn-rich phases present in the bulk and in the patina of a given building block. Reduced Mn species then migrate to the exposed surface of building blocks where they are re-oxidized via undetermined processes. Patinas developing “naturally” over time result from the alternation of wetting-reducing and drying-oxidizing cycles and appear to be composed of birnessite. Patinas formed after the 2003 fire result from this single accidental event and form a much thinner, heterogeneous, and discontinuous layer of poorly crystalline lithiophorite at the sandstone surface (∼ 0–150 µm compared to ∼ 300–600 µm for “natural” patinas). The lack of Mn-rich patinas on areas of Lunéville château is likely related to the lower Mn content of pristine sandstone blocks.

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Section: Discussionmentioning

confidence: 99%