Walk onto a thawing lake in spring and the surface can shatter into thousands of vertical glass needles, each one pointing straight down into the dark water below. They clink like wind chimes. They will also cut through boot leather. This is candle ice: ice caught in the act of falling apart along the lines it was built on. The story starts months earlier. When a calm lake loses heat to freezing air, the first clear sheet to form is congelation ice, grown not by snow piling on top but by water freezing onto the underside of the existing cover. Heat conducts up through the ice and escapes, so new crystal grows downward into the colder-than-it-looks water beneath. That downward growth is selective. Ice is hexagonal, and crystals whose lattice favors vertical extension outrun their neighbors in a slow competition called geometric selection. The losers get pinched off. What survives is a forest of long columnar grains, all standing on end, perpendicular to the surface, tips probing towar...