Cluess about Sparkles! (Refractive index, dispersion... WHAT?)

[velouriaL]

So I tried to do a search both on the board and on the web, but I''m still confused about what makes a colored get sparkly. Refractive index? Dispersion? Fire? What does it all mean?

I''ve always read that some cuts are sparklier than others... I know emerald cuts are not very sparkly because of the facet pattern, but what about others?

I understand that Demantoids are more sparkly than Tsavorites. Why? Are there another colored gems are particularly sparkly? Crysoberyls?

 

[velouriaL]

(clueless, even)