Emily Short has written several fractured-fairy-tale games with titles that are the names of materials: Bronze, Glass, Indigo, Alabaster, and probably others. (Another uncredited example game from the recipe book, "Pine", adapts the story of Sleeping Beauty; "Sand" is a scene from Cinderella—the Brothers Grimm version, which involves sorting peas and lentils.)
Based on these data I felt comfortable in concluding that she also wrote Onyx, a conclusion I just now confirmed using social media.