It is well known that iron and iron-bearing compounds can provide an UV screen for life. For instance, Martian regolithic dust, along with palagonite- type compositions, have specifically been suggested as a possible safe haven for life [1-3, 30-35]. Our experimental results demonstrate a large difference in the UV shielding capabilities of both minerals (Fig. 2). Whereas gypsum showed a much higher transmission percentage (with an error in the absorption coefficients of roughly 20%), jarosite samples, with a thickness of only 500 ìm, 20%), jarosite samples, with a thickness of only 500 μm, prevented transmission. Our mineralogical results complement other recent petrologic studies about shielding effects on Mars surface environment (e.g. basaltic dust, ) and have great astrobiological relevance as: a) jarosite typically occurs on Earth as alteration crusts and patinas and b) a very thin crust of jarosite on the surface of Mars would be sufficient to shield microorganisms from UV radiation.