These rocks are from Sterling Hill Mine in Ogdensburg, NJ (US). The peculiarity of these rocks is their fluorescence. They are composed of three minerals: willemite, calcite and franklinite, however just willemite and calcite are fluorescent. What it is also noticeable is they are phosphorescent as well; they keep glowing in the darkness a few seconds after the source of light has ceased. The best way to look at these specimens is in a dark place under Short UV light. Willemite shows a green colour and calcite orange colour. It is your chance to get a spectacular rock! Sterling Hill Mine is closed and the specimens found there are collector's treasures.