Hyalite Opal - Chalk Mountain Mine, Spruce Pine, North Carolina

Contributed by: Chris Clemens
minID: LYN-0W8
Date: May 20th, 2026
Locality: Chalk Mountain Mine, Spruce Pine, Mitchell County, North Carolina, USA (See on Mindat)
Size: 8.9 x 6.3 x 10.2 cm

Description:
Hyalite opal from the Chalk Mountain Mine, in Spruce Pine, North Carolina, provides a classic example of uranyl-activated green fluorescence, and is one of the most brightly fluorescent minerals. This specimen consists of glassy hyalite opal (opal-AN) on a light-colored granite pegmatite matrix. The opal shows brilliant green fluorescence under shortwave UV, and a bright green response under longwave also.

Interestingly, because the hyalite contains trace amounts of the element uranium, it is slightly radioactive.

Originally posted by Chris Clemens on Nature's Rainbows in 2016.

Fluorescence under shortwave UV light.

Fluorescence under longwave UV light.

Normal light.

Summary of luminescence responses:

Opal-AN (Mindat) (RRUFF)

• Fluorescence under Longwave (365nm Lamp/Mercury) UV light: Green
• Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Green