Humboldtine is exceedingly rare at the Francon quarry, where it has been found as bright yellow inclusions in quartz (Sabina, 1992, 1994).
Interesting accessory minerals include phenakite and euclase, as 2-3 mm crystals, and a fairly large amount or orange-brown humboldtine
. The humboldtine
is entirely natural and not the result of any chemical treatment of the specimens.