INVESTIGATION OF URBAN ROCK VARNISH ON THE SANDSTONE OF THE SMITHSONIAN CASTLE
Richard A Livingston, Carol A. Grissom, Edward Vicenzi, Zoe Weldon-Yochim, Nicole Little, Janet Douglas, Alexandre Fowler, Cara Santelli, Dorothea Macholdt, Diana Ortiz-Montalvo, Stephanie S. Watson
Bluish black, highly adherent patches have been observed growing on the Seneca sandstone of the Smithsonian Castle in Washington, DC. They are significantly enriched in Mn compared to the underlying sandstone, by a factor of 100, which suggests that microbial activity plays a role. The mineralogy is likely a mixture of birnessite and todorokite, which is also consistent with microbial activity. The thickness is estimated to be on the order of 250 nm, three orders of magnitude thinner than typical desert varnish, and the varnish lacks the significant clay component found in desert varnish. However, the rate of growth, 9 nm/a, falls within the range of 1-40 nm/a measured for desert varnish. Trace amounts of Mn are found in Seneca sandstone, but they do not appear to be the major contributor to the varnish, which implies that airborne particulate matter would be a significant source. Ambient air concentrations of Mn have been measured at 4 ng/m3 in the District of Columbia, but the concentrations at the Castle may be higher because of its proximity to a major roadway.
International Congress on the Deterioration and Conservation of Stone
September 6-10, 2016
13th International Congress on the Deterioration and Conservation of Stone
, Grissom, C.
, Vicenzi, E.
, Weldon-Yochim, Z.
, Little, N.
, Douglas, J.
, Fowler, A.
, Santelli, C.
, Macholdt, D.
, Ortiz-Montalvo, D.
and Watson, S.
INVESTIGATION OF URBAN ROCK VARNISH ON THE SANDSTONE OF THE SMITHSONIAN CASTLE, International Congress on the Deterioration and Conservation of Stone, Paisley, UK
(Accessed July 2, 2022)