Indentation hardness of phytoliths, dental tissues, environmental dust and quartz particles. Upper section: nano-indentation data presented here, band inside the box plots = median, box = 1Q = first quartile, 3QR = third quartile, end of the whiskers = minimum and maximum values; epoxy resin values used for embedding given as comparative. Lower section: published comparative data by Ang et al. (2010), Baker et al. (1959), Broz et al. (2006), Cuy et al. (2002), Erickson (2014), Lucas et al. (2013), Lucas et al. (2014), Mahoney et al. (2000), Sanson et al. (2007), Willems et al. (1993) converted following Chudoba and Griepentrog (2005), only mean, and minimum to maximum values were available; plant phytoliths: Am. mau. = Ampelodesmos mauritanicus, Av. sat. = Avena sativa, Bo. grac. = Bouteloua gracilis, Cu. mos. = Cucurbita moschata, Da. glom = Dactylis glomerata, Ph. aus. = Phragmites australis; dental tissues: Bi. biso. = Bison bison, Eq. caba. = Equus caballus, Ho. sapi. = Homo sapiens, Ov. ari. = Ovis aries, Po. pyg. = Pongo pygmaeus, Su. scro. = Sus scrofa.