What is inside the "weight element" brick? I own a few bricks that contain a weight inside of them. 52g according to Lego.



What exactly is inside of these bricks that makes them heavy?
I did the unthinkable!  ...I had to know.

I opened one of my two weighted bricks.  One of the two ends has a glued on cap that I've cut around using an utility knife. 



The piece of metal it contains fit almost perfectly in the cavity.  I don't know metals but it has a rainbowish kind of sheen to it.  Here's a close up:



I'm now gluing it back with super glue.