Investigations of Luminescent and Phosphorescent Calcite from the Middle Ordovician Tumbling Run Section, Strausburg, Virginia, USA

Calcite is one of the most common minerals at the earth's surface and has a tremendous influence on the carbon cycle, biology, surface and groundwater chemistry, oceanic, sedimentary and metamorphic systems. The “Tumbling Run Section” south of Strasburg, Virginia is a globally recognized locality consisting of a section of Ordovician black limestones which have pervasive calcite veins. These calcite veins are phosphorescence and luminescent in ultraviolet light producing a variety of colors such as purple which is extremely rare, yellow-green, and red-orange. Details regarding the causes of phosphorescence and luminescence in calcite are poorly understood. Potential causes of the optic responses in theses calcite vein could be due to minor or trace amounts of specific elements (e.g., Mn, U) or the incorporation of organic matter during deformation.

SEM investigation revealed many interesting features among samples including high porosity dissolution textures, complex clusters of euhedral Fe carbonates, distinct crystal populations, and negative crystals. Textural data indicate that at least one dissolution event has occurred in most samples and in some samples there is a reprecipitation event. EDS analyses (detection limit ~0.1 wt%) on calcite indicates that Ca is the only major cation present.

Minor elements or the incorporation of organic matter are ruled out as the cause of luminescence and phosphorescence in these samples. Trace amounts of Mn, U, REE and other transition metals may be the cause and an association with dissolution textures suggests optically active components were introduced during late stage diagenesis. Mineralogical investigations of these calcite veins provide insight into causes of variation of the phosphorescence and luminescence and may have implications for improving sensors and other optic technologies.