Siderite, Iron cabonate, FeCO3. Siglenlas mine, Nr. Llanidloes, Central Wales Orefield. There is very little left in the way of spoil heaps at this location, so to find this particular specimen was extremely fortunate. The rock is brecciated with pockets filled with siderite. One face is completely covered with siderite, with a bunch of well formed crystals in the centre. The crystals, even if they are very weathered, make identification much easier.