Calcium phosphate crystals frequently occur in normal urine with an alkaline pH (>7.0), but are also seen in people who form kidney stones. They are colorless and show great morphological variation. The crystals may occur as prismatic shapes, needle or wedge-shaped rods with usually blunt ends, and sometimes as star-shaped clusters (rosettes). These shapes are usually strongly birefringent. In addition, large, flat plates with irregular edges and granular structure can also be found. However, these plates are not birefringent.