the.com/rock candy

means A sugar crystal confection made by letting a saturated sugar solution slowly crystallize, often on a string or stick, into large, glassy chunks.

from The 'rock' is plain description — the crystals really do look and sometimes snap like translucent mineral rock, formed as sugar comes out of solution and grows into visible lattices over days. The method itself is old and widespread, with versions found in ancient South Asian and Middle Eastern sugar-making traditions long before it became a jar on a general-store counter. The word 'candy' traces back further, through French and Arabic, to a Sanskrit root for a piece of crystallized sugar — meaning rock candy's name describes almost exactly what it is in two different languages layered on top of each other.