Sindarin for Knife of extremely hard obsidian (glassy stone)

knife of healing of extremely hard obsidian (glassy stone)?

I think these are (sort of) the parts, but using multiple adjectives confuses me.)

cerf nan gôn heledhren dîr

I would say cerf na nestad morcheledh dhorn

I used the cognate of NQ. Moricalca. And I think dorn “tough, strong” would be better here.

Thanks!