Remnants of Tranquility
This page here is to give you the low down on all you need to know about this particular item. Mostly why it is valuable and why I felt like pointing it out to you. The only items that get their own pages like this are ones that you should definitely be looting and ones that require "other" explanation other than just vendor it. For each of these items there are two methods of selling them, the quick and cheap way which is through /bar or if you mouse over an item in your inventory the hotkey for bringing up barter on an item is Alt + Shift + left click. The other method is through the The Bazaar. To bring up the Bazaar it is Control + Shift + Left Click. Check the value of the item in both to determine which you'd like to sell it in.
Remnants of Tranquility are the group currency added in The Broken Mirror expansion. This currency is extremely valuable since it is used to purchase slot 5s for many different levels from the merchants in Plane of Health as well as slot 9s. I highly recommend you check out my whole TBM gearing guide for more on Remnants of Tranquility! Honestly that guide will have just about all you need to know on them so head over there if you plan to use them. If you plan to sell them definitely sell them in The Bazaar. These things are going to be very valuable for years to come.