These are sterling silver pendants set with faceted phosphorescent GAGG Lumogarnets. These garnets will glow in the dark after exposure to bright light, even normal white LEDs like a phone flashlight (though blue or UV will charge them better). The glow is quite bright at first, then fades to a lower glow that is longer-lasting, easily visible in a dark room for several minutes after charging!
GAGG is a lab created garnet which is increasingly used in scientific and medical equipment. It's new as a material, only commercially available for technical applications in 2014, and very new as a gem since we first brought it to the gem market in 2022. It is what we call a 'lumogarnet' - a lab created garnet with incredible fluorescence--and, rarely, phosphorescence! The ones with great phosphorescence we also call 'Firefly Garnet'.
That's right, these particular examples glow in the dark! They actually do their best to prevent that from happening because it makes them less effective for technical use, but every now and then growth goes wrong and a crystal will have some afterglow, and an even smaller percentage are also clean enough to facet into gems.
GAGG is a durable gem with a high hardness of 8 and no cleavage.
