"The ones they sell in the psychic shops are very pretty, though."
The prettiest crystal I ever had was an ultrasonic band one in a glass vacuum envelope with an octal base. It was a thing of beauty.
Until we decided to make it into the control element for an oscillator, accidentally applied far too much feedback, and it came right off its supporting wires.
Perhaps there's a marketing opportunity here finding old ones, putting them on stands and selling them as high efficiency radiation absorbers.