i would epoxy it and CLAMP it shut! yeah clamps. to make the crack disappear. epoxy does not work with large gaps. no glue does to be honest. should be minimal gap. glue has good strength when bonding stuff tight, its not a good "building material" since its so weak in bulk. and yes all types of ebony are quite brittle and crack prone in my opinion. I have cracked about 5 of these on purpose to get them off knives i've bought. I would never use any ebony type on my own handles. its just not good enough i think. ebonys are preeetty much my least fav woods. and they dont even look good. I have used ziricote which is also a black wood and its less crack prone and a tougher. turkish walnut can also get very dark with oils and its not brittle/cracky at all. its quite the opposite. its used in rifle stocks. its regarded as the very best material for rifle stocks even. and the most expensive. also all types of ebony i have encountered smelled very bad and unpleasant. this is reason enough to not use it imo. i'm not a pro knife maker or carpenter. but i have made about 15 or so handles, and have worked as a "cabinet maker"/furniture carpenter and also 10 years in repair/paint of everything wood. so ymmv.