Crystals found in Urine Crystals are divided into two categories depending on whether they are found in acid (<7) pH or alkaline (>7) pH. Types of Crystals: Normal Crystals in Acidic Urine Uric Acid: It is seen in acidic urine and pH must be <5.8 to form uric acid crystals Typically coloured either yellow or reddish-brown, but may be colourless. Often seen as a four-sided plate that may be thin or thick and laminate. Crystals may cluster into rosettes. Other forms are rhombic plates or prisms, barrel-shaped, thick cubes, oval forms with pointed lemon-shaped ends, and wedges. Occasionally, colourless six-sided forms resembling cystine are seen. Strongly birefringent when viewed with polarized microscopy Calcium Oxalate: Seen in an acid environment, but may also be found in neutral or alkaline urine Small and colourless. Large forms are uncommon. Dihydrate crystals are the most commonly seen. Appear as an envelope or square with a cross. Monohydrate crystals