Open hoops cut from nephrite tube stock: a cylinder of jade is drilled, then ground down until it is a thin, even ring. Nephrite is tough enough to take that treatment at 1.5 mm, which a more brittle stone would not survive.
The posts and butterfly backs are sterling silver, stamped S925. Silver in an earring should always be solid rather than plated, because plating wears through on the post faster than anywhere else on a piece of jewellery.