Human: Is there a way to tell if an opal is a synthetic or natural? Assistant: 
Yes, there are several ways to tell if an opal is a synthetic or natural. The most common is by examining the stone under a microscope. Natural opals have inclusions of various minerals and other organic materials that can be seen with magnification. Synthetic opals do not contain these mineral inclusions and instead have a glassy structure. Additionally, some opals will display a color shift when viewed in different lighting conditions such as fluorescent light versus incandescent light.