Color Characteristics of Blue to Yellow Beryl from Multiple Origins

Abstract

GEMS & GEMOLOGY SPRING 2020 Gem beryl is a significant gem species, including color varieties such as emerald, aquamarine, heliodor, goshenite, morganite, and red beryl. Blue to yellow beryl has been found in numerous locations, including Brazil, South Africa, Russia, Ukraine, Canada, Myanmar, the United States, Afghanistan, and China (Belakovskiy et al., 2005). Blue color in aquamarine and yellow color in heliodor are attributed to abundant Fe ions (Wood and Nassau, 1968). Fe ions are also present in all other color varieties of beryl, though Fe content is relatively low in morganite. Although discussions on the role of Fe ions in blue to yellow beryl are not new, they have mainly focused on crystal physics and chemistry. This article explores the color characteristics and chromophore ions of blue to yellow beryl using quantitative chemical and spectral analysis. The crystal structure of beryl is unique for having a peanut-shaped “channel” along the c-axis, and alkali ions in this channel interact with transition metal ions. Therefore, we will discuss the features of alkali elements and their roles in beryl color, based on analysis of the channel mechanism. This research was part of a series of ongoing studies on the color characteristics of beryl. MATERIALS AND METHODS Beryls from different origins were gathered and 14 of them with various color and alkali content were selected for this study (see table 1). They were classified in the following color varieties: goshenite (colorless to near-colorless), aquamarine (greenish blue to blue), green beryl (green to yellowish green), and heliodor (greenish yellow to yellow). With the exception of two faceted stones and one rough stone, the samples were