Vintage Rare Abalone Beads & Central Drop Adventurine (?) Pendant Necklace

This is such a stunning necklace. I can easily identify the main stones around the neck and those are polished abalone stones. I hadn't seen abalone polished into stones like this before. They're absolutely beautiful. However, when it comes to the center drop stone I'm not sure as to what it is. It is definitely stone because it's cold but it could be any number of types of stones. I think it's possibly adventurine. This is when you wish you had a presidium. please see the pictures as they are an essential part of the items description. All reasonable offers will be considered. This is a gently pre-loved item.