Even though you get it from drinking milk and yogurt people shouldn't be surprised to learn that calcium is a metal. After all, reading through the ingredients list on a cereal box there's iron and magnesium and others too. But the thing is that calcium isn't something most are familiar with as an object.
And yet, it really is a metal. On the moon it would make for a perfect metal to make, I don't know, a cell tower or something. It's very light and plentiful. Why the moon? Well, because there's no atmosphere or water there that could come in contact with our imaginary calcium tower. Either of those touch it and the calcium instantly sizzles and corrodes.
So keeping it in metallic form here on earth takes a little work. We've put this piece in a special gel that should do the trick. Your little plastic cube remains just as light as if it had been filled with gel the whole way!