Calcium oxalate dihydrate crystals have characteristic bipyramidal or prismatic shapes. Under the microscope, they often appear as envelope-shaped structures, with distinct and symmetrical morphology. The size of the crystals can vary widely.

The presence of calcium oxalate is rarely clinically relevant, but can be an indication of the presence of kidney stones. They also often occur in stored, old urine. Any form of calcium oxalate is polarizing.

In particular, spinach, rhubarb, beets, almonds and soybeans are high in oxalate.