Casper Mountain

Casper Mountain

I've wanted to take my teenage son fluorescent mineral collecting. He is interested in hiking the rugged, remote volcanic terrain located about 80 miles west of here. But as is often the case, our schedules didn't mesh. And the trip didn't materialize.

One evening my son was off work. It was late, dark, and my ultraviolet lamp batteries were charged. So, I suggested we head up Casper Mountain. It's a 15 minute drive. The land is mostly private. But there is a little public land next to a small, simple pegmatite. So off we went.

I didn't expect to find much. Maybe a little uranium ion activated material, which glows a weak green, could be found. But, this was a chance to get out and test the new lamp.

So, we parked next to the pegmatite. Put on our head lamps. And fired up the ultraviolet lamp. My older 4 watt lamp didn't put out much ultraviolet light. But the 18 watts from this new lamp was powerful. An intense, bright, blue light radiated from our clothing. It was so bright that discerning a weakly glowing fluorescent rock was difficult. And stumbling around in the dark, as one's eyes adjusted from the bright blue glow to the darkness was easy. I didn't have this problem with my 4 watt lamp. I must remember to keep the lamp pointed away from my blue jeans :>)

Cryptonite from outer space?

Once the lamp was off our clothing, and our eyes adjusted so that walking without falling was possible, the whole place lit up. I couldn't believe it! The brightest objects were brilliant green and they were everywhere.

Very bright uranium activated minerals filled the fractures in quartz and feldspar. The more transparent quartz specimens were very attractive. The glowing material, inside the quartz, presented a three dimensional matrix.

This caught my son's attention. Was he holding something created for a science fiction movie? He promptly grabbed the hammer and started reducing larger rocks to specimen size, a dangerous proposition in the dark without protective eye ware. I didn't expect to find much, so I hadn't brought safety glasses along!

Bright orange fluorescent caliche.

Among this green material were rare, flat, slightly crumbly pieces that glowed a bright orange. It was so startling that I first thought it must be a lichen rather than a mineral. It was almost as bright as sodalite but with more variability. I tossed it in the bag.

It's amazing what can't be seen at night when collecting. Although the fluorescent minerals are easy to spot. Much of the geology is easily missed. When I pulled that flat piece out of the bag the following morning, I was shocked. I hadn't seen a rock like that. The glowing material was mineral rather than vegetable.

Calcite vugs in highly altered serpentinite.

So, at daylight, up the mountain I went. Walking over the hill from the pegmatite, I found an outcrop of this material. Turns out it was a highly altered, brecciated, serpentinite with zones of veins, vugs and calcite fillings. That's a unusual rock for Wyoming. I took time to photograph the adjoining pegmatite. And I scheduled another night time prospecting trip.

That night I fired up the lamp with my son in tow. We headed over the hill away from the pegmatite. The whole place lit up with oranges, whites, creams, pinks, and greens. You couldn't put your hand on the ground without touching something fluorescent. After spending several hours wandering across the outcrop, my son asked if this is typical fluorescent mineral collecting, as he only had the two nights experience! It was typical for this location, but I'd never experienced it like this before.

The multiple colors, variety of hues and intensities from calcite, impressed me. The weathered serpentinite glowed a bright orange. The calcite ranged from varieties of pastel white, to green, salmon, peach and hot pink. Intensities ranged from bright to the subtle.

Carbonate vugs.

This variety is due to several convergent factors. The serpentine is highly altered at this location. It's intruded by a pegmatite producing local metamorphosis. And a portion of both the serpentinite and the pegmatitie were hydrothermally altered. Throw in a little surface weathering and much variety is the result. The greatest variety occurs in a weathered zone nearest the pegmatite.

I liked this variety a lot. My son preferred the extra-terrestrial looking material:>) This material has a beautiful phosphorescence. When the lamp is shutdown, the green and blue-white fluorescent material continues to glow together. After about a minute the green glow subsides leaving a bluish-white glow that lingers for a time.

The pegmatite yielded a few pieces of feldspar with a dull, cherry red glow. Beautiful feldspar is found around Pikes Peak that glows like this. How lucky can one man get in a single evening! And I found a few small quartz specimens with a yellow to rosy peach glow.

On the way home, we radiated some Precambrian road cuts looking for more. These cuts were a-typical for the evening. Not a single glowing mineral was found. Only a few sweet clover blossoms illuminated the scene.

Cherry red fluorescent feldspar.

The surprise and excitement generated while collecting fluorescent rocks is appealing to me. Even the most unpromising locations can yield beautiful specimens and wonderfully satisfy an old geologist like myself.