The Glass Dunes are a relatively small area of the southeastern Rusanan desert which, as the name implies, is coated in layers of glass.
The glass is formed by the native glass dragons (which are drakes, not dragons, but never mind) and local scholars theorize the reason to be anything from mating displays to the dragons making the very glass they coat their bodies in, to the dragons creating their own art like humans.
The glass forms uneven dunes and valleys and is streaked in a variety of colors from impurities in the sand. It's also often riddled with cracks and broken pieces are scattered everywhere. Whenever sand blows in, it gets melted and added to the dunes.
Because the glass is so webbed with cracks it doesn't reflect light too much, but it still gets hot there- Which the glass dragons seem to love, they can often be found basking in the dunes in even the hottest of days.
Glass from the dunes is a popular choice for mosaics and trinkets since it doesn't have to be made or colored. It can, generally, be safely gathered as long as you don't disturb any brooding glass dragons. (It's also widely believed that taking too much / pulling pieces out of the ground will anger the dragons, so only loose chips are gathered)