I had seen a vase on the Antique Roadshow that was carved out of a Rhino horn the appraisal was thousands of dollars - My friend has something that looks similar. It is more intricate carving on it. Color is very similar - this is a little darker patina. I have pictures - He would like to sell it if it is worth money. If I could send you the picture I took of the one on The TV show and the one that he would like to sell you will see why I think it is rhino horn as well. - It is not perfect - but still a beautiful vase.
This plate is 10" in diameter with handleholds. Blue and white pattern has pomegranates about the edge and a floral/tree bush pattern in the center. Mark on the back looks like K or R in a diamond shape.