'Rod like structures' (incrusted filamentous bacteria?) of As sulphide composition in a 'mucus' (also amorphous As2S3) presumed to have been secreted by arsenate and sulphate reducting bacteria.


                                                                                                                                                false coloured by Eric Condliffe

The sample above is from a profile taken over the active geothermal system in the Eastern Geothermal Field in the Uzon Caldera, Kamchatka Penninsula, Russia.  The sample was collected at~ 35cm depth, and it was in contact with a fluids at ~ 65oC, pH ~ 5.4.
Similar structures are expected to exist in many active arsenic sulphide forming environments (e.g., New Zealand, Japan)