A couple years ago I was attempting to wipe a hard drive in a spectacularly low level manner: I'd taken the platters out and was dragging neodymium magnets over them. This was probably because the hard drive itself had ceased to function and I wanted to ensure the data wasn't readable. But the platter ... shattered. Prior to that, I hadn't been aware that HD platters were sometimes made of glass - I thought they were all made of aluminum. According to Wikipedia, glass is now pretty much standard in laptop hard drive platters.
I'd mentioned the experience of having the platter shatter in my hands to several people. Most were sceptical - for which I don't blame them. But I guess it's made me a bit defensive about it, to the point that I feel the need to blog about it.
Here's a photo of a platter from a IBM Travelstar 6 GB 2.5" laptop hard drive. I was decommissioning a very old laptop and slid one of the platters into a ziplock bag (I learned the last time that breaking it with your bare hands can lead to injuries) before breaking it with a pair of oven pads. It even created a semi-artistic effect, although the plastic of the bag significantly detracts from that.