Trace Element Content and Optical Cathodoluminescence of Kyanite

Abstract

Kyanite is a common mineral in Al-rich, medium- to high-grade pressure rocks and an important resource for the refractory industry. We determined the characteristics of optical cathodoluminescence (CL) and minor and trace element concentrations of kyanite by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS). Six kyanite samples from basically two lithotectonic environments: (A) metamorphic, coarse-grained quartz–kyanite segregations derived from metasediments (Bahia, Selbu, Naxos) and (B) metamorphosed Al–Si-rich (argillic) alteration zones related to island arc magmatism (Kola, Nasafjell, Halsjoberg) were characterized by their trace element content. The kyanites contain considerable V, Ti, Fe, and Cr, whereas Mn, Mg, Na, K, and Ca could not be detected. Group A contains high V (83–182 ppm), high Ti (15–198 ppm), low Fe (435–1465 ppm), and low Cr (23–312 ppm); Group B is characterized by high average Fe (≥2,360 ppm), and low average Ti (≤14 ppm). The Halsjoberg and Nasafjell samples are also poor in V (1–60 ppm). The Kola sample is strongly enriched in Cr (mean of 994 ppm). All samples display red CL near 700 nm, commonly with lamellar variations in intensity. The intensity of the red CL can be correlated with Cr3+, and is distinctly lower in group B with higher Fe2+, known as a CL quencher. Besides red CL, the Naxos sample shows lamellae of violet and blue CL, which can be correlated with high concentrations of Ti4+.