From Delgar

Zir, the City of Glass, is the former capital of Al-Uqh. It takes its nickname from the shimmering crystal spires that make up the majority of its structures. These structures were created by dragon fire in a war long ago, when the red dragons were fought to extinction. Since then, well defended by nigh-impenetrable crystal walls and attracting visitors from all over to see the majesty of the city, Zir grew into a hub of global trade, serving as the gateway between the western and eastern halves of Delun.

Zir's major industries are trade, tourism, and manufacturing, with its most valuable and unique export being dragon-glass, fire-blown by dragonborn artisans from the unique sand found only on the edge of the Sand Sea, as hard as steel and considerably lighter, not to mention very sparkly and pretty.