As pretty much everyone has said it's because of the rarity of it, the variety of uses and that it's got no real replacement for many of it's uses (in many cases you can get some of the properties).
Add to that it's easy to store, and doesn't degrade over time, so it's almost perfect as a way of keeping your "money" safe as it won't generally devalue too much, and won't be affected by things like a housing market crash
Add to that it's easy to store, and doesn't degrade over time, so it's almost perfect as a way of keeping your "money" safe as it won't generally devalue too much, and won't be affected by things like a housing market crash

