The New Jerusalem decends from Heaven or from above to the earth. This is a city of I think 1500 sq miles that will become the capital of the world.
You can see it will be a very fancy place. Now we are doing good to build out of granite & marble. But then they will be using a transparent gold to pave the streets. The gates of the city will be made out of what traditionaly have been precious stones. Of course even now crystals of different colors are not as rare as they use to be. People are able to grow them out in their garage. If you go to a gem show you can buy very large pieces of what use to be precious stones.