When you think of expensive gemstones, what comes to mind? Most people think of the Big Four: diamonds, emeralds, rubies and sapphires. However, it might surprise you to know that there are ...

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.

Meline: A pearl is one of the most complex gems to assess the value of. One factor is whether it's natural or cultured. Natural pearls are harder to find, making them worth more money. The vast ...