Lewm
when we just mount a crystal out in space on a cartridge or tonearm there is no electrical energy source to set the crystal into resonating,
In my view there are 2 possible sources of excitation for the crystal -
1. Any resonance generated by the cartridge when playing a record
2. Electromagnetic radiation from the cartridge generator.
Whether these are significant enough to excite the crystal - someone else can do the maths.
the EMI emission from the crystal can alter the behaviour of other EMI floating around in the vicinity
This is the basis for the "looney" brigade selling crystals for PC's to make you feel better. Whether it is a process of absorption of EMR or emission to change the fundamental frequencies of electromagnetic radiation is open to debate.
Remember a doctor was struck off by the medical association for suggesting smoking was injurious to health in the late 1800's and Florence Nightingale took 30 years to convince the medical fraternity that clean bandages and fresh air was helpful in wound treatment.
I try to keep an open mind in these matters.