Simulated Black Opal Titanium Hypoallergenic Stud Earrings. These Stud earrings are handmade with Simulated Black Opal Cabochons and Grade 23 Hypoallergenic Titanium. They are extremely durable and the post is "bend proof". Available in 6 and 8mm diameters. Comes with two sizes of Titanium backs for preference. Shipped in gift box. Opal is the birthstone for October.