Fluorescence of Limestones and Limestone Components

The fluorescence of a series of limestones has been investigated; the relative fluorescence intensities of these limestones differ by a factor of 10. With UV excitation, the fluorescence spectra of these limestones exhibit two distinct peaks, one blue and one red; the relative magnitude of the blue peak is larger for more fluorescent limestone. The limestones were digested, allowing for isolation of different limestone components, which are acid-extractable organics, bitumen, and kerogen. With the correlation of fluorescence spectra and intensities, it has been established that the acid extract fraction produces the blue peak in the rocks. Concentrated bitumen produces red fluorescence, contributing to the red peak of the rock. Generally, the limestone kerogens are found to possess very low fluorescence, in contrast to carbonaceous shale kerogens, and probably do not contribute to rock fluorescence.