Cressevain Marble
To the far east on the island of Inai there is mountain range that separates the plains from the northern swamps. These mountains are the Cressevain Peaks are are the tallest, most dense mountain range in all of Bannoria. These mountains are full of harvestable materials like ore and stone. One material that has proven to be more valuable than first believed is a particular metamorphic rock called Cressevain Marble.
It is a black colored stone with veins of white going through it. The marble is surprisingly durable and has become a favorite material for the merchant kings to decorate their homes with. A quarry deep in the Cressevain mountains carefully chisels large blocks of this stone from the mountainside and hauls it further east to reach the dwarven stronghold of XX where they sell it to material traders. As one can imagine, the expense for this stone is astronomical, which is why even the smallest of statues made from Cressevain Marble can fetch prices into the hundreds of gold... if they can find the right buyer.
The richest people in the world build monuments from this stuff. Where do you get it and what special properties does it have?
I like the look of black marble, but I definitely would not be able to afford it in your world! :D