Silica sinter from Puhipuhi, Northland, (4 million year old system) with layers rich in red cinnabar (mercury sulphide, HgS). Cinnabar does not dissolve readily in rain water, so poses no environmental threat.
Microprobe element maps showing the distribution of mercury and silica in a 1.6 mm x 1.6 mm portion of the Puhipuhi sinter. The colour scale shows high mercury as purple and low mercury as mauve or stippled. Cinnabar seen as thin coloured bands on the mercury map, with these same bands highlighted in the silica map indicating low levels of silica and high levels of mercury.
