corundum, inclusions.5, gems

Lea continues his microscopic investigation of minute crystals enclosed within minerals, adding observations to those reported in his earlier 1869 paper. He describes the forms and occurrence of microscopic crystalline inclusions and considers their identification and relationship to their host minerals. Particular attention is given to the value of careful microscopic examination for recognizing well-developed crystal forms that are invisible or indistinct to the unaided eye. The study is of historical gemological interest as an early investigation of mineral inclusions by microscopy, anticipating the later importance of internal features for gemstone identification and for interpreting mineral growth and formation.