SWIM has observed this occurrence and has even collected, dried and used these crystals.

In SWIM's case, this occured while using STB methods to basify fumarates.  SWIM had a layer of sodium carbonate solution and a layer of naphtha in a container under fairly cold conditions.  This was most certainly jungle-spice.  It seemed as though the jungle-spice was attracted to the naphtha layer but was unable to dissolve.  The layer seemed to start out as an oily layer floating atop the aqueous layer, under the naphtha layer.