The Mn-analogue of cronstedtite, a serpentine. Guidottiite has an ideal composition of (Mn2Fe3+)(SiFe3+)O5(OH)4. Guidottiite-2H1 and -2H2 were reported by Wahle et al. (2010) with random interstratified polytype intergrowths and stacking disorder common. The sample comes from the Kalahari Manganese field, South Africa, and forms from hydrothermal solutions.