A man poses for a picture to show his rings of gold, silver and bronze on his fist in Zamfara, Nigeria April 21, 2016. (Photo by Afolabi Sotunde/Reuters)

Crocoite is a mineral consisting of lead chromate, and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment.

A model walks the runway at the Christian Siriano X Lane Bryant Collection at United Nations on May 9, 2016 in New York City. (Photo by JP Yim/Getty Images)

Ender Moreno looks for gold at La Culebra gold mine in El Callao, Bolivar state, southeastern Venezuela on March 1, 2017. Although life in the mines of eastern Venezuela is hard and dangerous, tens of thousands from all over the country head for the mines daily in overcrowded trucks, pushed by the rise in gold prices and by the severe economic crisis affecting the country, aggravated recently by the drop in oil prices. (Photo by Juan Barreto/AFP Photo)

In this Thursday, May 8, 2014 photo, Iranian coal miners push metal carts to be loaded with coal at a mine near the city of Zirab 212 kilometers (132 miles) northeast of the capital Tehran, on a mountain in Mazandaran province, Iran. International sanctions linked to the decade-long dispute over Iran's nuclear program have hindered the import of heavy machinery and modern technology in all sectors, and coal mining is no exception. (Photo by Ebrahim Noroozi/AP Photo)

A gold mine worker displays gold in a local mine in Al-Ibedia locality at River Nile State, July 30, 2013. (Photo by Mohamed Nureldin Abdallah/Reuters)

A model gets final adjustments back stage before participating in a plus size fashion show in Nairobi, Kenya, October 7, 2017. (Photo by Baz Ratner/Reuters)

A worker works on a “Transformers” replica on the outskirts of Shanghai, June 18, 2014. Li Lei, owner of a small factory, uses his spare time and money to build “Transformers” replicas for rent or sale. The new Transformers movie, which is premiering later this month, has brought the factory many new orders, according to Li. (Photo by Aly Song/Reuters)