A large specimen of halite crystals from Poland that have this amazingly pretty blue-green color from inclusions of malachite the halites picked up as they grew! You would swear this is a specimen of green fluorite from some new locality, unless you were to lick it an realize that it is SALT (but do not lick it - natural halite specimens can harbor bacteria). Dave Stoudt was stationed in Poland for 10 years, and had the opportunity to obtain specimens from old and generally closed localities, in addition to some interesting contemporary things many of which did not reach the general market. Searching out retired miners in their homes, he got some neat things and made up a Polish minerals collection that shocked me!