corundum, inclusions.5, gems, inclusions, history of microscopy

Lea reports microscopic observations of minute crystals enclosed within larger mineral specimens, emphasizing that such inclusions may themselves possess recognizable crystalline forms and provide evidence concerning the formation of their host minerals. He describes microscopic crystals observed in several minerals and considers their shapes, arrangement, and possible mineralogical identity. Of particular gemological importance is the early application of microscopy to the study of inclusions in transparent minerals, demonstrating that internal features could reveal information not obtainable from external examination alone. The paper anticipates the later systematic use of inclusions in gemology for mineral identification and for interpreting the conditions and sequence of crystal growth.