Warning #ACOTAR Spoilers ahead!
This necklace screams faerie wine and body paint. An elegant crown frame boarders this substantial blue Sapphire. I imagine Feyre is wearing something sheer and draping during her time spent as Rhysand's play-thing. So, I mimicked that in the draping of the chain. The moons and stars represent Rhysand's title and the droplets on the ends of the chain are all the tears Feyre shed in her cell while held prisoner to Amarantha.
About the stone: "The magnificent and holy Sapphire, in all its celestial hues, is a stone of wisdom and royalty, of prophecy and Divine favor. It is forever associated with sacred things and considered the gem of gems, a jewel steeped in the history and lore of nearly every religion. To the ancient and medieval world, Sapphire of heavenly blue signified the height of celestial hope and faith, and was believed to bring protection, good fortune and spiritual insight. It was a symbol of power and strength, but also of kindness and wise judgment. Today Sapphire is still a Stone of Wisdom, a royal stone of learning, mental acuity and psychic activation, a seeker after spiritual truth. Its pure Blue Ray brings order and healing to the mind, lending strength and focus, and an ability to see beneath surface appearances to underlying truths and to utilize that knowledge."