This is a large cabinet specimen purchased by Arnold Hampson in 1972 in Santa Eulalia. There are two very distinct generations of Calcite, which are called "Mariposa" (butterfly) habit. The first generation are scalenohedral crystals measuring 3 to 4cm and are covered by glitterly iron-oxides and/or Siderite. The second generation overgrows the first and are simple yellow rhombic Calcite. The first generation is highly fluorescent red, but is hard to through the oxide coatings. However, flipping the specimen over you will see the intense red patterns of growth under shortwave UV.
It is a beautiful specimen in which the photos do not give justice. The special edition on Santa Eulalia in the Mineralogical Record describes these Calcite crystals and the Mariposa habit including a few photos. On the outer edge are two broken off crystals, which do not detract from the overall appearance. In order to extract these from the wall, it was inevitable.