Looks more like iron oxide.
If it was ferrous oxalate instead, you can do a potassium ferricyanide (part B of a cyanotype kit) test - add a drop of an acidified (may not be required since you are already adding oxalic acid) solution of it to a bit of this slurry, if it results in a blue color (that of Prussian blue) then either you have ferrous oxalate by mistake from the supplier or you have ferric oxalate that is partly converted to ferrous.
:Niranjan.
If it was ferrous oxalate instead, you can do a potassium ferricyanide (part B of a cyanotype kit) test - add a drop of an acidified (may not be required since you are already adding oxalic acid) solution of it to a bit of this slurry, if it results in a blue color (that of Prussian blue) then either you have ferrous oxalate by mistake from the supplier or you have ferric oxalate that is partly converted to ferrous.
:Niranjan.