Limonite and anthosiderite minerals. Limonite (orange) is a field name for various iron oxides and hydroxides. It is found in surface oxidation zones of iron deposits, or as a residue of carbonate and silicate breakdown in tropical conditions. Anthosiderite (purple) is composed of Quartz and Goethite minerals. It is a pseudomorph, meaning the minerals have encrusted or infiltrated a pre- existing structure. This sample measures 75 millimetres across.