Calcium oxalate

Occur in several shapes but are most easily recognized when they form small, octahedral, envelope-like shapes

When present in large numbers, strongly suggest ethylene glycol poisoning or, rarely, short bowel syndrome, hereditary oxalosis and oxaluria, or high doses of vitamin C

Important in evaluation as potential constituents of calculi

Cystine

Perfect hexagons, sometimes alone as flat plates or as overlapping crystals of varying sizes

Diagnostic of cystinuria, a rare hereditary cause of calculi

Magnesium ammonium phosphate

May resemble coffin lids or quartz crystals

Often occur in normal alkaline urine or in urine of patients with struvite calculi

Uric acid

May be diamond- or needle-shaped or rhomboid, although uric acid may be amorphous

Often present in acidic, cool, highly concentrated urine

May indicate mild dehydration in neonates or tumor lysis syndrome in patients with cancer or renal failure