Yes I agree that with a sharp edge & very bright light even inner core of rhino with heavy melanin & calcium deposits can have a 1mm of translucency. This is harder on very rounded surfaces of course.
Also this is not a black core but does have years of dirt without the care of oiling, which also promotes the translucency, hence it being more common with age.
One of my points was, identyfying horn by burning as well as bieng destructive doesnt rule out other horn types, they all smell of burning hair.
Beneath the years of dirt no oiling it may be translucent & indeed if set on fire.
But the clear formation structure of this jambiya grip, is rhino horn, I grew up in a family working at importing timber world wide, we had boxes of recognition keys for identyfying timber end grain under magnification. I recognise that this is no timber
& the only horn with fiberous orange peel effect on the cross cut end grain is rhino!