You can disenchant any gem you already own and obtain some Rare Flickering Dust depending on the quality of the gem disenchanted.
1. Click the Forge icon on the main menu panel:
2. Switch to the Workshop tab and click the Disenchant menu:
3. Hover your mouse over an enchantment. Click the vortex icon to open the disenchant interface, where you can see how much dust you'd get for disenchanting a particular gem:
4. Click "Disenchant" to confirm your choice. You can also dispel multiple gems if you have an active Premium status:
Rare Flicketing Dust is used for gem crafting. Use the dust you obtained from disenchanting to create a new gem:
1. Switch to the Workshop tab of the Forge and click the Craft menu:
2. Hover your mouse over a gem. Click the "+" icon below the one you wish to craft in order to see how much Rare Flickering Dust is needed to create that particular gem:
3. Click "Craft" to confirm the crafting. You may use all of your Flickering Dust available to create many pieces of that gem if you have Premium status activated:
Note that creating gems of certain quality requires certain technologies to be researched in the Academy. Visit the Academy's "Blacksmithing" branch and scroll it further to the right to see all of the technologies available - there are four of them, the same as for combining gems. Each technology allows you to create gems of higher quality.