I bought The Perilous Dark supplement at the last wargames show I attended (if you remember what they were) in November 2019.
The Perilous Dark was the last supplement for Frostgrave First edition, but is generally compatible with Frostgrave Second Edition.
One of the scenarios involves weirdly glowing crystals. I bought a pack of Crystals (cast in resin) from Bad Squid Games. Originally they were for Malifaux (Rasputina)
They were cleaned up and glued to Renedra 25mm diameter bases. Milliput was used to blend them in, and Woodland Scenics fine ballast glued on top.