When I grew up collecting minerals in the 1980s, these calcites were already fading from contemporary markets. The sharp and yet fuzzy-looking rhombohedral calcites on a bit of sulfide matrix were classic Naica material of the time, and I have a fondness for them still. Not fancy, not gemmy, but somehow appealing for the form and style, this is just a classic Naica calcite and a classic calcite style overall. It is slightly fluorescent orange, due to manganese.