National Geographic : 1951 Nov
© National Geographic Society 4 Rainbow Colors Hide Within These Prized Collectors' Items Fluorescence is not present in most minerals; in others it exists only in specimens from certain localities. Cumberland, England, yielded the lavender fluorite. Tan and white common opal came from Nevada, and white calcite from New Jersey. Ektachromes by Willard It. (ulver + Fluorescence Works Its Magic; Rocks Glow Like Neon Lights Calcite turns a fiery red, fluorite an intense blue. Pastel green mingles with blue in opal's depths. Min eral colors differ under fluorescence because atomic vibrations send out varying wave lengths of light. Invisible ultraviolet rays "trigger" this reaction.