Simply theoretically, could one create Synthetic Opal with a different compound than Silica?
My idea was that since Aluminium Oxide is very similar in properties to Silicon dioxide, one could theoretically make synthetic opal in a similar way by using Alumina trihydrate or some other compound. The particle sizes would probably have to be changed etc but after fine tuning I think it could make some very nice gems and maybe even be cheaper and way easier to produce than synthetic opal.