gems, beryl, emerald

Lewy reports chemical and geological investigations of emeralds from the Muzo deposits of New Granada (Colombia). From analyses of several emerald specimens, he found silica, alumina, glucina (beryllia), and small quantities of other constituents, but was unable to detect sufficient chromium to account for their green color. Instead, he identified a small amount of organic matter whose abundance appeared to vary with the intensity of the green coloration and proposed that this organic substance, rather than chromium oxide, was responsible for the color. Drawing on observations of the Muzo occurrence, where emeralds occur in association with fossiliferous limestone, Lewy further argued that the crystals had formed by a “wet” process, through deposition from aqueous solutions. His conclusions concerning both emerald coloration and formation were controversial and were subsequently challenged, particularly his rejection of chromium as the principal cause of color. A more extensive version of the study appeared in Annales de Chimie et de Physique in 1858.