Sugar crystals are a real treat for someone with a sweet-tooth. The good news is they're also not too difficult to make at home.
Definition
Sugar crystals are clumps of sugar that form on a base after cooling sugar-saturated water. They're also known as rock candy.
How to Make
Boil water and stir in sugar as it boils until the sugar stops dissolving. Stir food-coloring in for colored crystals. Then tie a piece of yarn to a pencil, making sure the yarn nearly touches the bottom of a glass jar but doesn't actually make content. Pour the solution into the jar and lower the yarn into the jar. Let the pencil rest on the mouth of the jar. Finally, set the jar somewhere where it won't be disturbed and allow the crystals to grow to desired size.
Chemical Composition
Glucose and fructose, which are found in foods, have a chemical composition of C6H12O6. Sucrose, or table sugar, has a composition of C12H22O11.
Molecular Structure
Sucrose has a hexagonal form. For a cool 3D model, check out this link from Indiana University: iumsc.indiana.edu/morphology/sucrose.html .
History
According to Dryden & Palmer, producers of rock candy since 1880, sugar was used as a medicine and preservative until the 1700s. Rock candy in particular is referenced by the poet Rumi and the playwright Shakespeare in the play Henry IV.