Tiffany Stone - Brush Wellman Mine, Delta, Utah

Contributed by: Chris Clemens
minID: JA3-XFQ
Date: May 24th, 2026
Locality: Brush Wellman Mine, Spor Mountain Mining District, Thomas Range, Juab County, Utah, USA (See on Mindat)
Size: 163 x 9 x 169 mm
Weight: 457 g

Description:
Tiffany stone is a complex rock composed of opalized fluorite with bands and veins of chalcedony, manganese oxide and bertrandite. The only known source for this rare material is the Brush Wellman beryllium mine, Spor Mountain, near Delta, Utah, where it is mined for its beryllium content. Due to its swirling colors of purple, lavender and cream, Tiffany stone is a popular lapidary material and is often cut into cabochons and beads. Less known is that it is also brightly fluorescent under UV due to its fluorite and opal content.

The example shown here is a sawn slab that displays best under shortwave UV . It shows an unusual garden-like pattern of predominantly green fluorescence due to the opal component, which contains trace amounts of uranium (uranyl-activated fluorescence), as evidenced by the low level of radioactivity emitted by this specimen (approximately 200 cpm). The pale blue fluorescence is due to the fluorite component.

Under shortwave UV (254 nm), a mossy green pattern of fluorescence is seen due to the uranyl-containing opal content, while fluorite accounts for the pale blue response. Following exposure to shortwave UV, an interesting pattern of blue, cream and yellow phosphorescence is seen.

Originally posted by Chris Clemens on Nature's Rainbows in 2022.