Fluorite, Calcite, Willemite - Hull Mine, Castle Dome Mountains, Arizona

Contributed by: FMS Admin
Date: May 7th, 2026
Locality: Hull Mine, Hull Mine group (Rialto Mine group; Hull group of claims; Rialto claims), Buckeye vein group, Castle Dome Mine group, Castle Dome Mining District, Castle Dome Mountains, Yuma County, Arizona, USA (See on Mindat)
Weight: 3 lb

Description:
Arizona is home to some great fluorescent rock collecting (as well as some of the best birding in North America). Great mines are scattered throughout the state, from the northwest corner near Flagstaff, clear to the southeast area in the mountains near Portal and Tucson. The Hull Mine is in the southwest area of the state, near Yuma, and provides some great examples of fluorite, calcite, willemite, and other minerals. This rock is a nice sized one, weighing in at almost 3 pounds. I have found the material seems to like shortwave plus midwave the best. Longwave tends to obscure the willemite; midwave provides just enough to bring out the fluorite

For a little background on the mine and the area, here is some information from one of those who is resurrecting this great fluorescent locale:

"The Hull Mine runs beneath the stark Castle Dome Mountains north of Yuma. It is one of 300 mines gouged from the Earth in this lonely corner of Arizona. The old silver mine dates to the 1880s and was purchased in 2014 by Allen and Stephanie Armstrong, owners of the adjacent Castle Dome Mine Museum.

Their original plan for the Hull was to do what they did at Castle Dome, preserve a slice of Arizona history by restoring old buildings and salvaging equipment and materials. Everything changed once they got a look at the wonders inside the mine.

In January, tours into the Hull Mine began. Visitors are driven down the main passageway to a wide corridor, 100 feet below the surface. From there it is a short stroll to the end of one drift. At first the high walls look no different than any others towering overhead. But when the lights are clicked off and UV lights hum to life, it is only seconds before the rocks begin to bleed color.

The minerals setting the walls ablaze at the Hull are calcite, fluorite, scheelite, willemite, barite, hydrozincite, aragonite and selenite."

Looks like a great place to explore and collect in the very near future!

Originally posted by Fire Viper on Nature's Rainbows in 2018.