The fire retardancy of pure hydromagnesite and other natural mixtures of hydromagnesite and huntite minerals has been tested using forest species samples of Phillyrea latifolia L., collected from a wildland/urban interface (WUI) zone near Athens. Three different methods were employed for this study. The first was thermal analysis (TG, DTG, SDTA), using samples of few mg, relatively slow heating rate (10 °C min^-1) and atmosphere conditions of: (a) O2, in order to favor complete combustion, (b) N2, to isolate pyrolysis and (c) air, in order to approach real combustion conditions. The second was a laboratory-scale method, based on a specially constructed preparative-scale DTA, using samples of few grams, static air atmosphere and low heating rate (0.5 °C min^-1) to favor smoldering combustion. The third was a new flame spread test, using 10-12 g samples formed into a train mold. Some common forest fire retardant media (i.e. DAP, MAP, AS), as well as a widely used commercial forest fire retardant (i.e. Phos-Chek D 75-F) were also studied as means of comparison.