Where to find rare crystals?

[The A.W.G.]

I have no idea where to find them. I looked in many GRE facilities and dark hollows but I only found crystal statuettes and crystal dust.

[kaishark]

Just searching for the rare christals can take hours. The easiest way is to do Harpers regular Mission. By finishing it you'll get two rare christals - and they are counting for the bounty too.

[Amb. MARTIF PHARTI]

There are five crystal mounds at Heron Renegados street level, about 7 mounds on the outskirts of Houndfield, and at least 3 military convoys that have a mound each. But, the above reply is definitely faster. I can show you the ones that i've found in the open if you like just send a FR. Cheers.

[leel duck]

This dude saved me hours of headache tryna farm those stupid cores, thank you for this tip. Never woulda thought to check.