Calcium Oxalate (Monohydrate and Dihydrate) Crystals on Urine Microscopy The calcium oxalate crystal is found in urine with acidic pH and has two forms- monohydrate and dihydrate. Mnemonic: 1 line [|] monohydrate (black arrows) 2 lines [X] dihydrate (red arrow) Dr. Telma Lemos @TELMALEMOS10 #Calcium #Oxalate #CaOx #Crystals #crystalluria #Urine #Microscopy #clinical