Opal on mars, there may be some expensive necklaces come from this discovery...

Thread title wrong ( you said HiRISE, not CRISM - I've edited it for you).

Wrong forum ( Mars Express for some reason, not MRO - I've moved it for you)

My bad Doug, it was very rushed. Thanks for fixing it for me!

Opal is after all just a variety of hydrated silica and most of it is definitely not gem quality. It is even secreted by microorganisms and grass (not that I suggest that this is the origin of Martian opal).