Hello and thank you for posting your Omani Khanjar. I have a picture of an almost exact same hilt. The Ruler often gives these weapons as gifts underlining the importance of this badge of office and Iconic item in the Omani tradition.
It is quite acceptable to get the weapon as clean as you can...if you wish. It is usually worn on a white dishdash so that if it is covered in silver oxide it would be a bit of a mess, so the locals clean it but don't be alarmed by this...It soon tarnishes and after a few months quickly reverts to its patina... The use of felt on the back is to keep it clean etc.
Deciding what the hilt is can be difficult on a foto...If it is Sandalwood it should have that perfume. Give it a rub to warm it up and smell it... If it doesn't smell of perfumed wood its not sandalwood. (I think it may be by the way)
The best test as has been already described is with a fone or powerful torch which will light up Rhino like luminous spaghetti straws.
Giraffe ( Giraffe horn called confusingly Zraff Hindi is African Giraffe) is another possible but it does not light up like rhino ..in fact it is rather dull. but takes mass silver pins in the same way as does Sandalwood! If you tried to hammer in this many silver pins into a cow horn or ordinary wooden hilt it would split!
My guess without the simple tests is.. it could be Sandalwood or Giraffe..and it could be Rhino!! and to help along the discussion I've been out and found one identical (nearly) below and for further reference you may find an answer in my thread The Omani Khanjar at Forum Library.
The one below is Giraffe.
Ibrahiim al Balooshi.