ARE ICICLES SINGLE-CRYSTALS

During the winter of 1977-1978, about 60 icicles were examined between crossed polarizers (12 inch sq.). Thus, specimens more than a foot long could be examined. Thin sections parallel and normal to the long axis were used. The thin sections (1/8 inch-1/4 inch) were prepared by using a warmed aluminium plate to form plane-parallel surfaces by melting. The growth rate of selected specimens was from less than 1 inch to more than 14 inch/day. A wide variety of textures was observed. Crystallite size ranged from less than 0.03 to more than 8 inch. It was found that single crystal regions as large as 8 inch by 1 inch can be produced in icicle growth. Crystal orientation was checked in some cases (using the optical interference figure) and in no case was the c-axis found to be near the icicle axis. Representative photographs are presented, comparisons are made with ordinary ice-cube texture and the growth mechanism is discussed. It is interesting to observe that nature, apparently without too much effort, regularly grows millions of ice crystals of a size which most crystal growers would be proud. Suggestions are made for the use of the simple techniques described for further studies of icicles by students interested in the phenomena of crystallization. © 1979.