X-ray Photoelectron Spectroscopy study of so-called “Larimar”, blue pectolite from the Dominican Republic

Abstract

ABSTRACT:A detailed analysis was undertaken of the X-ray photoelectron spectra of the blue variety of pectolite known by the trade name Larimar from the Dominican Republic in an attempt to elucidate the origin of the blue colour. The survey scan confirmed the chemical composition of pectolite. The O 1s showed a complex set of bands associated with Si-O-Si, Si-O-(Na,Ca) and OH in the crystal structure of pectolite. From the possible elements suspected to cause the colour, such as Cu, Fe, Mn, and V, only Cu and Fe were observed above the detection limit of the XPS instrument. For the first time about 0.02 atom% of Pb was observed in one sample, while another sample from the same block showed the presence of 1.05 atom% Sb. The possible presence of [Pb-Pb] 3+ pairs can act as a chromophore analogous to that observed in the bluegreen feldspar variety amazonite. This would explain the till now unexplained optical band at 630 nm as well as part of the high hydroxyl concentration. Though other chromophores cannot be excluded, the observation of Pb adds a new possible explanation for the blue colour of Larimar.