I should have thought about this topic earlier.
Here are some photos of the assorted kryptonite props I have acquired or made. These are essential for my Batman and Lex Luthor costuming --
Those crystals were made by casting resin in molds formed over real quartz crystals. I have a bunch more -- I might post additional photos later.
The following jumbo lightstick (sorry it's not lit in the photo) is going to come in handy when my Lex Luthor needs to fend off Kryptonians at Dragon*Con --
I have a nice "sheet" of kryptonite (mold was made over a sheet of short quartz crystals) that I want to back-light. This is a project for later.