Bytownite basalt ( Bytownite feldspar) is another variation of the common Basalt rock. Basalt tends to to be a dark, fine, crystalline igneous rock and has a number of different variations. Bytownite feldspar is a calcium rich member of the Plagioclase family. The mineral was first described in 1835 & named for Bytown (now Ottowa) where it was found in Canada. High quality transparent examples are used to make faceted stone in the jewelllery trade. In these examples the phenocrysts are green & opaque & set in a basalt matrix. The specimens come from Cumbria, UK and are supplied in a white card tray with a label.