Beryllium oxide is used as an electrical insulator because while it doesn't conduct electricity, it does conduct heat very well, which allows it to cool the components it is isolating electrically. It's quite glassy, like a real ceramic, not powdery like many metal oxides. I don't know if that's a basic property of the material, or whether it's somehow vitrified in a matrix of some other ceramic material. The package warns that while this insulator is harmless as supplied, it should not be modified in any way, presumably because of the danger of releasing beryllium oxide powder (beryllium is very toxic in powdered form where it can get into the body).
Want to see one in action? Here's a picture of what looks like this exact insulator being used to make a fun little gadget, a tabletop fusion machine. I have it on good authority that this is not like cold fusion, that it really does work to produce fusion. (It's not a practical source of power because of the tiny amounts of fusion that actually occurs, but it is said to be the only low-cost source of neutrons if you need them for some reason.) It sure would be fun to tell our personnel manager we're building a fusion reactor in the unused cubicle: I wonder what the employee manual has to say about that....
Source: eBay seller billw87
Contributor: Theodore Gray
Acquired: 8 November, 2002
Text Updated: 11 August, 2007