Dryden and Palmer White Rock Candy Crystals (1 Pound Bag). For centuries, Rock Candy has been recognized as having marked therapeutic and preservative qualities. In fact, in the West, sugar was used only as a medicine or preservative until - in the middle of the 18th century - people "discovered" it made a sweet treat as well. Rock Candy is made by a process of crystallization, the same process that produces quartz and diamonds in nature - with a different ingredient, of course. It is made by breaking apart the sugar (sucrose) molecular crystal lattice and then allowing it to re-form in conditions that produce larger, purer crystals. In fact, it is the purest form of sugar available, because all impurities are excluded as large crystals form.