Regarding the Star Gate Chair there is a handler that operates it that lets people in and out. Once you set for into the third step you disappear to a destination somewhere. You do not need to be sitting in the chair unless you are a handler. There are and can be another portal chair somewhere else or just a location where you are teleported there though the star gate frield.
The floor is a heavy metal. The chair is made of a type of metal the same with the platform. To me it looks harder than iron. You know if you see a piece of iron against a wall somewhere well it reminds me of iron slabs put together I think it is a standard platform chair for recon, handling and star gate. But that crystal one is really something.