What kind of stone is this, struvite or calcium oxalate?

Hello. From the photo, your cat has a stone. To determine its nature, urine tests and microscopy are needed. Most cat urinary stones are struvite, but proper tests are required for an accurate diagnosis.

If it’s struvite, treatment acidifies the urine with medication to dissolve the stone and prevent bacterial infection. In the diet, reduce phosphorus and magnesium to limit stone formation.