What makes one mineral so precious or costly compared to another?

first off it depends on what type of rocks your talking and or asking about. for example rubies emralds saphires and dimonds are considered precous stones because they can be used as a soort of currancy so to speak but mainly because they can be converted quickly to cash by them being liquiasssests.

if you need more information look up things like "the importance of precious stones and the stock marketand money feild "