Facets are uncut gems that are received as the rewards of completing Diplomacy Writs. Most Writs have as a reward a choice of a particular kind of Facet or a choice of one of two kinds of Facets. Some Facets are only available from writs in one particular Diplomatic Prestige Center, where others are available in several. Consult with the Writ list and look at the rewards to determine where to go to do a Writ that rewards you with the type of Facet you are seeking.