Hyalite Opal Geode from Mexico

Contributed by: Chris Clemens
Date: Apr 28th, 2026
Locality: Candelaria Mine, Moctezuma, Moctezuma Municipality, Sonora, Mexico (See on Mindat)
Size: 7.5 x 5.8 x 7.6 cm
Weight: 270 g

Description:
This is a hollow, rhyolitic, geode nodule half containing a botryoidal, bubbly mass of colorless hyalite opal and small quartz flowers, from the Candelaria Mine, Moctezuma, Sonora, Mexico. Under shortwave UV the hyalite fluoresces bright green, and the hollow geode shell provides an aesthetic setting. The quartz is not fluorescent but picks up the green light from the emission of the brightly glowing hyalite. The hyalite also fluoresces dim green under longwave UV (not shown). Due to the uranyl-activated mechanism of green fluorescence, this specimen emits a low level of radioactivity, approximately 40 cpm, about twice the natural background level.

Originally posted by Chris Clemens on Nature's Rainbows in 2017.

Fluorescence under shortwave UV light.

Normal light. Interior of the geode.

Normal light. Side 2. Exterior of geode showing rhyolitic shell.

Summary of luminescence responses:

Opal-AN (Mindat) (RRUFF)

• Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Green