NOTE: Some information contained in this post is incorrect.
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Here is a little bit of advice. If your microwave oven is crushed into a pile of dust and shredded metal you should not snort it up your nose. Bits of it are poisonous.
The magnetron, which generates the microwave energy, has a sintered ceramic insulator that is made from beryllium oxide. During use it is inert and harmless but if it is crushed and the dust is inhaled you can get berylliosis, an incurable disease of the lungs.
There are other electronics items that contain beryllium oxide as well as other nasties, so to be safe make sure all of your e-waste is recycled. Here at Ecotech Services we can fix or safely recycle your microwave oven of course. Or we can recycle just the magnetron. And other types of e-waste. Give us a call.
[Edited 13 August 2015]