Epitaxial Marcasite on parallel growths of sharp Arsenopyrite crystals showing the so-called “key” shape. They are on matrix, with small white Calcite crystals, small Siderite crystals and leafy Muscovite aggregates. Minas da Panasqueira / level 2, Aldeia de São Francisco de Assis, Covilhã, Castelo Branco, Centro  Portugal (1997)