The photomicrograph below features druse crystals in a cross-section of the stem of an angiosperm, or flowering plant. Most druse crystals found in plants are made of calcium oxalate, which is also the compound that most frequently forms kidney stones in humans.

Druse crystals are a common occurrence in many plants and are usually granular or star-like in shape. Crystal formations that appear needle- or spear-shaped are referred to as raphides. Both are thought to deter herbivory, and a number of species of plants are poisonous to humans, as well as animals, due to the high calcium oxalate content.

The word crystal has ancient origins and is derived from the Greek word krystallos meaning the ice. Early civilized cultures believed that transparent crystals of rock quartz were formed from ice so deeply frozen that it could not be melted. Common everyday forms of crystal include sugar, table salt, quartz, moth balls, ice, gemstones, and vitamins.