It's probably just the name given to that type of brick due to the metallic effect on the brick (though that doesn't explain the red brick in my link), I know very little about them so I'm unable to comment further,there are however more knowledgable members on here when it comes to bricks who may be able to help.
Also, it may be worth using the search box located at the top of the screen as there may well be brick threads on this forum.
Hope you get the answers your looking for Bob
