Nice Opals.
I would have to say and this is a tad esoteric, The Arc Of The Covenant is the most powerful!
Check this link out (
http://www.stormchaser.ca/Caves/Naica/Naica.html) ...makes me wonder what else is inside our Mother Earth, this example could be just a small piece!
The only crystal I currently own is a, green, purple and clear quartz obelisk, given to me by my partner.
My partner has the accompanying Amethyst sphere. There is a magical and powerful connection between them.