Alexandrite is a variety of Chrysoberyl which, at 8.5 on a scale of 10, is just under Sapphire (Corundum) in hardness. That quality makes it a very good stone for rings. In addition to that feature, alexandrite is very beautiful. Because it is also very rare, it is quite expensive.
Here I have set a very pretty alex in a 14K gold bezel that is mounted on a sterling silver shank. The shank has been carved and engraved to provide further visual interest on both sides of the setting.