It has been determined the thermal behaviour at high temperatures of an iron aluminum arsenate mineral first described in
the location of La Serena Valley, Extremadura, Spain, which expands until 1173 K contracting later and softening at 1653 K
and full melting at 1773 K. The DTA/TG experiment only detects some rearrangement with an endothermic at 1173 K due to the
mica mixing. The mineral is a scorodite variety mixed with micaceous clay which has been found as aggregates of pyramidal
crystals associated with quartz, wolframite, molibdenite, cassiterite and other secondary minerals in the pegmatite of the
San Nicolas mine. The chemical composition, the physico- chemical characteristics such as density and hardness, as well as
the thermal behaviour has allowed to conclude that this mineral can be an Al-enriched scorodite (mansfieldite): (Fe, Al) AsO42H2O mixed with illite from the scorodite-mansfieldite series.