corundum, inclusions.5, ruby, sapphire, spinel, aquamarine, beryl, emerald, gems

Sorby and Butler investigate the internal structure of rubies, sapphires, diamonds, and other minerals by microscopic examination, using inclusions and growth features to interpret the conditions under which the crystals formed. They describe minute cavities, enclosed crystals, and structural irregularities visible within transparent specimens and compare their character and distribution in different minerals. Particular attention is given to rubies and sapphires, whose internal features provide evidence of successive stages of crystal growth, and to diamonds, in which inclusions and structural characteristics are likewise examined. The authors argue that microscopic features preserved within crystals can provide important evidence concerning their origin and formation. The paper is an important early contribution to the systematic microscopy of gemstones and helped establish the study of inclusions and internal growth structures as a means of investigating mineral genesis.