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.

Tucked beneath the back of the stairs at the Ramada by Wyndham Tucson, 777 W. Cushing Street, Eritrean-born Huruy Zerzghi ...