“…While ferrihydrite is the predominant form of iron in anaerobic non-sulfidogenic environments ( Lovley, 1991 ), other more crystalline Fe(III) (oxyhydr)oxides can be more abundant in other environments such as soils, shallow aquifers, sediments, and the subsurface ( Cornell and Schwertmann, 2003 ). More recently, a range of Fe(III) (oxyhydr)oxides has been identified in geothermal environments, including sulfide chimneys and microbial mats at various deep-sea hydrothermal vents ( Kristall et al, 2006 ; Toner et al, 2012 , 2016 ; Lin et al, 2014 , 2016b ), and acidic terrestrial hot springs ( Kozubal et al, 2012 ). In sulfide chimneys and seafloor sulfide deposits at hydrothermal vents, two-line ferrihydrite, six-line ferrihydrite, lepidocrocite, akaganéite, goethite, and a biogenic Fe(III) (oxyhydr)oxide have been identified ( Lin et al, 2016b ; Toner et al, 2016 ).…”