Diamond and emerald brooch by Lacloche Frères, French, c. 1927-1930. Made of white gold, platinum, emeralds, brilliant-cut diamonds and stained chalcedony. This brooch is in the shape of a stylised cypress tree. The diamonds are set against stained chalcedony to form areas of contrasting pattern and reflection. Black onyx was popular for Art Deco jewelry. It is rare in nature, so stained chalcedony was often used in its place.
( Frankly I've never cared for those with the diamond added but this is a good example. If you own an old cameo it is good to gently wipe it with a good quality oil, such as olive oil, about once a year. These shells do dry over time and can crack which takes away from the beauty as well as the value.)jw