Abstract: The tubular structure that has been proposed for endellite [Al2(OH)4Si2O5·2H2O] will contain considerable space not occupied by the solid phase. Based on the tubular dimensions which have been reported for this material, void space of 30 to 40 percent of the total volume of massive endellite would be anticipated.
Experimental determination of the void space in several samples of an endellite specimen by means of density measurements made on water-saturated samples indicates that the massive mineral contains 10 percent or less void space. It is concluded that endellite does not exist in a tubular form.
When endellite dehydrates to form halloysite [Al2(OH)4Si2O5] there is no appreciable change in the gross volume of the material. The massive halloysite formed, however, contains more than 40 percent void space which is refillable with water. It is hypothesized that endellite may exist in the form of laths with some displacement of the fundamental layer structure. When the endellite dehydrates the laths undergo considerable shrinkage and distortion to give the structures observed in electron micrographs and shadow-cast replicas.