ice cubes in domestic refrigerators have been reported. The ability to grow ice spikes in a controlled environment has prompted a small number of investigations by the researchers in the Physics Department of the California Institute of Technology under the direction of Kenneth G. Libbrecht into the conditions needed for the spikes to form. Mechanism of formation Naturally occurring ice spikes, often in the form of circular ice candles or polyhedral ice towers (usually triangular), are occasionally found in containers of frozen rainwater or tapwater. Water expands by 9% as it freezes into ice and the simplest shape of an ice crystal that reflects its internal structure is a hexagonal prism. The top and bottom faces of the crystal are hexagonal planes called basal planes and the direction that is perpendicular to the basal planes is called the c-axis. The process begins when surface water nucleates around irregularities where it meets the container wall. If the c-axis of the first crystal to form is not vertical, the basal plane intersects the surface along a line perpendicular to the c-axis and ice needles tend to propagate across the surface along this line. Simply put, the surface freezes from the edges inward, so that only a small surface hole remains unfrozen. The crystallite curtains tend to join at an angle of 60 degrees and so the hole is often triangular. The continuing freezing of water that is below the surface ice then slowly pushes the remaining water up through the hole. Reaching very cold air, the edge of the extruded water freezes while remaining liquid in the center. more freezing below pushes more water up, the edge freezes, and so on. If the rate of extrusion of water is the same as the rate of freezing at the lip of the hole, then this process is continually repeated and successive layers form an upward-growing tube of ice. The formation of ice spikes is related to the shape of the water body, the concentration of dissolved impurities, air temperature and circulation above the water. Spikes that grow from a crystallite formed below the surface of the water may project from the ice sheet at a steep angle, rather than perpendicular to it. The ice spike process is rare - more commonly the surface freezes over entirely, and as water under the surface freezes it pushes all of the surface ice upward. Small ice