Every week you can buy up to 5 Stellar Glass from Cheri Ring in Tria. You can find her next to the Grand Hall portal at the center of Tria. Each Stellar Glass costs 200,000 Mesos. You can create a Gem Dust Chest with 10 Obsidian Essence and 1 Stellar Glass. Each Gem Dust Chest allows you to get 200 Gem Dust of a specific color of your choice.