Casper Mountain

The Mountain

Casper Mountain.
  • my son’s off work
  • it’s late and dark
  • and the new ultraviolet lamp is charged

Fifteen minutes away, up Casper Mountain, is a small pegmatite. It’s a great time to check out the new lamp and the pegmatite.

Lamp Light

At the pegmatite, we fired up the new lamp. Compared to my older 4 watt lamp, the new lamp’s 26 watts is extremely intense.

Once our eyes adjust to the darkness, I couldn’t believe it! Bright, vibrant green fluorescent rocks were everywhere.

Some of the more translucent quartz contained a 3D matrix of bright, illuminated fractures and fillings. Very unusual! Almost surreal. Could it be cryptonite from outer space? It captivates my son.


Occasionally, there’s a flat rock with a bright mottled orange yellow glow. Couldn’t tell what it was in the dark. A mystery rock?

Day Light

serpentinite outcrop casper mountain
Serpentinite outcrop.

The next morning I examined that mystery rock and was shocked. I hadn’t seen a rock like that in Wyoming. So back up the mountain I went.

Walking over the hill from the pegmatite, there’s an outcrop of this material. Turns out it’s a highly altered, brecciated, serpentinite, with veins, vugs, carbonate and siliceous fillings. Neat!

Back for More

That night my son Isaac and I visit the serpentinite outcrop.The whole place glows with a subtlety and complexity not seen in the pegmatite.

Oranges, whites, creams, pinks, and greens swirl in various intensities and combinations. You can’t put your hand on the ground without touching something fluorescent.

I’d never experienced collecting fluorescent rocks like this. The multiple glowing colors, hues and intensities impressed me:

  • caliche is a mottled bright yellow orange
  • calcite glows from pastel white, to blue, green, salmon, peach and hot pink
  • bright green silicates fill fractures
  • intensities range from bright to the subtle

This variety is due to several convergent factors:

  • the serpentine is highly altered
  • it’s intruded by a pegmatite
  • and a portion of both the serpentinite and the pegmatite are hydrothermally altered

Throw in a little surface weathering and much chemical variability is the result. The best fluorescent material occurs in a weathered zone near the pegmatite.

This material has a 3 phase phosphorescence. The green and blue-white fluorescent material phosphoresce together. After a minute, the green glow subsides leaving a bluish-white glow that lingers for ten minutes or more. Then that gradually fades to a dull yellow.

vuggy-serpentinite-wy-fluorescentHeading home, a quick stop at the pegmatite yields a few pieces of albite with a dull, cherry red glow. And a few small quartz specimens with a yellow to rosy peach glow.

How lucky can you get in a single evening? And so close to home!

For me, collecting fluorescent rocks creates surprise and excitement. It harkens back to a childhood time before fluorescent lights, tvs, and today’s countless glowing devices illuminated our lives.

Back then cold fire, especially from a rock, was simply magical. All the best museums had fluorescent collections which rivaled the dinosaurs for popularity. You waited in line to view them! And I waited.

Today, it’s just a quick drive up the mountain. No waiting and I can stay as long as I want.

Even an old geologist like myself can still feel the magic. Am I entering my second childhood? If so, maybe it’s not all bad. 🙂