Fluorescent Mineral Database

A new secret project! Trying to create a nice Fluorescent Mineral Database (FMDB), which would be searchable by mineral, locality, and luminescence properties. Also making it easy for people to contribute with their own specimens!

Hyalite-Coated Chalcedony and Fluorite, SK Star Claim No.2, Juab County, Utah

Contributed by: Chris Clemens
minID: D5T-A7F
Date: Apr 15th, 2026
Locality: SK Star Claim #2, Thomas Range, Juab County, Utah, USA (See on Mindat)
Size: 83 x 45 x 93 mm
Weight: 113 g

Description:
This interesting and unique fluorescent specimen looks like something you would expect to find in an underwater coral reef. Collected from the SK Star Claim No.2 in Utah's Thomas Range in Juab County, this piece consists of a coralline aggregate of chalcedony and fluorite (verified by XRD analysis), coated with a brightly fluorescent layer of hyalite opal. This specimen was collected by the claim owner, Shaun Rasmussen, some time between 2015-2018.

The SK Star Claim No.2 was discovered by Shaun Rasmussen and Krisann Morrill in early 2015 and is featured in an article in the Nov-Dec 2020 issue of the Mineralogical Record. The claim exploits a mineralized fault in a vuggy section of the Topaz Mountain Rhyolite located in the southern area of the Thomas Range, approximately 40 miles to the northwest of the town of Delta, Utah. In addition to producing these unique fluorescent specimens, the SK Star Claim No.2 is also notable for producing black topaz crystals and other minerals.

Picture 1. In the first photograph, taken under long wave UV (365 nm), the hyalite shows a bright green response, accented by small (? 2 mm) crystals of an unidentified mineral that fluoresces bright blue-white and shows white phosphorescence.

Picture 2. Under short wave UV (254 nm), the hyalite shows a brilliant, monochromatic, green, fluorescent response, significantly brighter than the longwave UV response. The green fluorescence is activated by trace amounts of uranium, in the form of the uranyl ion present in the hyalite and is evidenced by the mild radioactivity emitted by this specimen at a rate of approx. 300 cpm.

Picture 3. When viewed under visible light, the pale beige-colored chalcedony and pale purple fluorite can be clearly seen.

Originally posted by Chris Clemens on Nature's Rainbows in 2024.

Picture 1. Fluorescence under longwave UV light.
Picture 1. Fluorescence under longwave UV light.
Picture 2. Fluorescence under shortwave UV light.
Picture 2. Fluorescence under shortwave UV light.
Picture 3. Normal light.
Picture 3. Normal light.
View showing the mineralized fault on the SK Star Claim No.2.
View showing the mineralized fault on the SK Star Claim No.2.
Shaun Rasmussen removes overburden as he works his way into the fault.
Shaun Rasmussen removes overburden as he works his way into the fault.
Krisann Morrill works the upper end of the fault.
Krisann Morrill works the upper end of the fault.
Sunset over the SK Star Claim No.2.
Sunset over the SK Star Claim No.2.

Summary of luminescence responses:

Opal-AN (Mindat) (RRUFF)

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

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