Most notably: Golden Delicious and Opal. These varieties may seem indistinguishable on the surface since they are both yellow ...

Opal, often regarded as one of the most dazzling minerals, can develop within a variety of natural structures, including petrified wood, bones, and even seashells. This specific piece of wood ...

Following is a transcript of the video. Narrator: High-quality black opal can cost over $10,000 per carat, making it one of the world's most expensive gemstones. But mining black opal isn't easy.