You could try suspending the bone ash into IPA, assuming it doesn't react, then use a dropper to apply the solution on freshly cleaved mica and letting it naturally dry. You could try to speed it up by heating it on a hotplate @90 C, inside a fume hood. If the ash forms a viscous enough solution with IPA, spin coating it on the mica at 2-3k rpm may also work. 

Is the end goal to be able to AFM the bone ash particle clusters?

Thank you for the suggestion Tanuj, will try IPA or ethanol. Yes we are studying the crystal agglomerates and individual crystals.