and what about Ammolite ?
Ammolite is the mineralized remains of an Ammonite, the predecessor of the Nautilus (see old post).
Limestones containing various fossilized shells may exhibit bright iridescent colors notably red and green. This organic material is known as ammolite, korite, lumachella or fire marble, depending on its origin, structure and market.
jewelry tips: Natural ammolite is a 3.5 - 4 on the Mohs scale and is extremely delicate and brittle but triplets with protective clear quartz or spinel caps increase the hardness to 7 to 8.5, making the stone more durable for jewelry