Every item as a different value. As some things are more rare than the other and some are more valued than the other. Here's the exchange rate for currencies used. The issue with finding good value is finding a place that takes the currency. All values are measured by gram.
Dust - 0gd
Gold Dust - Main measurement.
Platinum Dust - 100gd
Meteor Dust - 1000gd
Comet Dust - 100,000gd
??? Dust - 1,000,000gd
Gold - 1gd per 1mm diameter
Quartz - 5gd > 10gd
Crystal - 10gd > 50gd
Sapphire - 20gd > 150gd
Ruby - 50gd > 400gd
Emerald - 100gd > 700gd
Jade - 150gd > 900gd
Lapis lazuli - 200gd > 1200gd
Topaz - 300gd > 2000gd
Amethyst - 500gd > 3000gd
Obsidian - 1000gd > 5000gd
Diamond - 2000gd > 10,000gd