Abstract: Control of Cathodo-Luminescence of Dolomite by Iron and Manganese

Bernard J. Pierson

Manganese (MnII) is considered the principal activator of luminescence in carbonates and it has been suggested that a minimal amount of 1,000 ppm manganese is necessary to produce a detectable luminescence. Iron (FeII) is the inhibitor of luminescence. To investigate the possible connections between the concentrations in manganese and iron and the luminescent properties of dolomite, a quantitative study of the cathodo-luminescence of that mineral was conducted; 86 samples of dolomite from a variety of environments and ages (Cambrian to Cretaceous) and a wide geographic distribution (North America and western Europe) were analyzed petrographically, using a luminoscope coupled with a photomicroscope. Selected samples were analyzed chemically by arc spectroscopy, atomic absorption, and electron microprobe.

The results of these analyses show that iron and manganese concentrations in dolomite increase and decrease together with greater variations in the iron content. A luminescent emission is observed for concentrations in manganese that are surprisingly low; as little as 100 ppm manganese is present in highly luminescing samples. However, iron (FeII) inhibits the luminescence in dolomite when its concentration reaches 10⁴ ppm or 1 weight % MnII. Above that level, no luminescence is observed, whatever the concentration in manganese. This relation suggests that iron, in concentrations higher than 1 weight %, is the major control of cathodo-luminescence in dolomite.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma