Some of the finest crystals of Wulfenite come from mines in Arizona and adjacent Sonora, Mexico.
Wulfenite is Lead Molybdate Pb[MoO4], and it is a secondary mineral found in the oxidation zones of Lead (Pb) deposits. It was named after its discoverer, Austrian Jesuit mineralogist Baron Franz Xavier von Wulfen. Wulfenite is soft with a Mohs' Hardness of 2.75 to 3 and brittle, so it cannot be used to make gemstones. Also, given that these soft, beautiful crystals contain Lead, they are also poisonous, and you should definitely wash your hands after handling them.
Wulfenite has a specific gravity of 6.8, so it is unusually heavy for a transparent or translucent mineral. Despite the rich color of the crystals, they have a white streak when scraped on an unglazed ceramic plate.
This uncommon mineral is highly prized by collectors because of its unique lustrous, tetragonal, tabular (flat, table-like) crystals which can range in color from yellow-orange to a fiery scarlet. Most Wulfenite crystals are very small, and large ones like these that I photographed at the Arizona-Sonora Desert Museum are very valuable.
The Red Cloud Mine here in Arizona is renowned for the deep orange-red color of the Wulfenite found there. Attractive crystals of Wulfenite can also be found here in Pima County at the Old Yuma Mine in the Tucson Mountains and the Total Wreck and Hilton Mines in the Empire Mountains.
If you are interested in seeing these and other Wulfenite specimens, visit the mineral display at the Arizona-Sonora Desert Museum. If you wish to purchase some Wulfenite, many nice (but expensive) specimens are for sale at the huge Tucson International Gem & Mineral Show, which runs from January 27 to February 12 at many locations around Tucson.