Ultraviolet (UV) light ("black light") reveals residual color patterns in fossil mollusk shells that would otherwise go undetected. UV light can also excite certain shell layers in different ways, as shown in this image of the inside of the two valves of a fossil Caribbean Spiny Jewel Box (Arcinella arcinella). (Photos of the valves under natural light are given for comparison.)
While most of the internal surface of the valves glow a bright purple color, both adductor muscle scars and the pallial line (mark where the mantle muscles were attached in life) fluoresce a greenish hue. The color differences we see are most likely caused by the distinct compositions of the shell microstructure in these areas. (For the UV-light photos I used a Kobra Black Light Flashlight 100 LED of 390–395 nanometer peak wavelength. No Photoshop was used to enhance or modify the colors.)
Comments