Discovery of the Quartz Pseudomorphs After Apophyllite

Summer Storm claim, Custer County, Idaho, Part I (goto Part II, goto Part III)

The Search

If you read the article on the discovery of the deposit of the heulandite and mordenite of the Rat's Nest claim, you will know what brought me to explore in this area of Custer County, Idaho. While searching for that original mordenite occurrence, I walked over the this area following the occurrence of agate. The first time, I overlooked the pseudomorphs, which were not obvious, but visible enough that I should not have missed them. Ample evidence that just because you didn't find anything at a location, or if someone (everyone?) tells you that there is nothing in a certain area, but you are curious and interested anyway--go exploring there. If that doesn't turn up anything, give it another look some other time!

I discovered the heulandite and mordenite deposit that became the Rat's Nest claim in September, 1999. That discovery just fueled my feeling that there were good things in this area. After the heulandite, then disocveing the original mordenite deposit in the same large area, I had to keep looking. There was one more occurrence that had to be found--Norm Radford had found a specimen of quartz pseudomorphs after apophyllite while searching the area after looking at the original mordenite location. That trip had been 45 or more years previously, and he could not recall the specifics on the mordenite occurrence, and even less of the location of the pseudomorph find.


Quartz pseudomorph after apophyllite, one of the uncommon crystals with smooth surfaces, found on the surface, 3.5 cm high, Summer Storm claim, Custer County, Idaho.

Quartz pseudomorph after apophyllite, a group of crystals with smooth surfaces, found on the surface, the white crystals are groups of "rice grain" quartz, 22 cm across, Summer Storm claim, Custer County, Idaho.

The Discovery

I knew they were in the area, but my searches around the two known zeolite deposits were coming up empty. On April 26, 2001 I ventured back into an area near Antelope Flats (the flats are surrounded by volcanic rocks). On that day I was actually interested in finding a good piece of fortification agate (sacrilege!) or a good piece of a quartz geode, or of course anything else of interest. After wondering around the hills, I finally came across a piece of a geode section lying on the surface. The crystals lining the geode were the pseudomorphs! Fantastic! After getting over the thrill of finding the first specimen, a careful search turned up a few more pieces. I was mad at myself for not finding them a few years ago, but realized after looking diligently, that they were not abundant and most of them were not easily recognized. They were scattered widely, and most were dirty. The volcanic rock was highly decomposed and the surface was mostly a clay (very sticky when wet) and most of the pieces had a coating of this dirt on them. There also are more pieces of geode sections with the boring small quartz druses, or an ugly spiky quartz and mordenite surface than there are pseudomorph sections. With the few pseudomorphs hiding in the dirt and amongst the common geode pieces, it was easy for them to stay hidden. I had to look carefully over a lot of country to find a few pieces.

The occurrence was interesting, it was a condition that would save a lot of time and mining expense if it was the same situation at the Rat's Nest claim. The lava flow containing the geodes was now the top of a series of eroded ridges. The occurrence was about the length of a mining claim and 100-200 feet across. The lava flow is about 6 feet deep, and sat on top of volcanic sandstones/siltstones, the same as the Rat's Nest claim. This one has the advantage though of the overlying volcanic sandstones having been eroded away.


Quartz pseudomorph after apophyllite, specimens from the large tube, left crystal is 6.5 cm high, cluster on the right is 14 cm high, Summer Storm claim, Custer County, Idaho.

This is not the location where the original specimen came from, because Norm had not ventured that far in his wanderings that day (Incidentally, I have since found where the original piece was found, but that area doesn't appear to be worth any effort in looking more or mining.) The original specimen is what prompted me to look, but I was now looking at a new mineral find. Agate hunters had often roamed the area, but they didn't take much away, the agate is the common gray to slightly bluish gray color, some shows good fortification/banding, but it isn't popular and mostly still lays on the ground out there, baking in the hot summer sun and freezing in the winter's sub zero temperatures. Some of the early agate collectors dug some holes where there were "outcrops" of white quartz and agate, but these holes are now slumped in and are just shallow depressions that lie there as silent testimony to the ambition of the rockhound. Fortunately for me, the agate collectors who searched this area did not recognize the potential of those odd white pyramid-shaped quartz crystal "coatings" or had no interest in mineral specimens.

The next day after the discovery (April 27th), I prospected the occurrence further west and discovered two outcrops of the lava flow on either side of a narrow dry wash. These were the only outcrops. The one on the north side of the wash had a number of the ugly geodes with a white quartz rind and a spiky, rough inner surface with mordenite on some. These aren't attractive when fresh, and exposed, they are ugly brown from all the fine dirt they collect.

The outcrop on the south side of the wash was much more interesting. It had a half a geode showing that was lined with the pseudomorphs over an inch in length. Topping that off, the other half of the geode was laying down the wash a short distance. Fortunately, being quartz, they are nearly indestructible in the surface environment, and when cleaned up, they were still in excellent condition. Another opening was found above and to the left of that one. This proved to be tube-like and about a foot across. It was a bit gross though, it had been the home of a packrat at one time (his skull was resting outside at the base of a sage bush below it). Packrats are not tidy about certain things, and the inside of the cavity was a large deposit of what was probably very good composted guano.

Looking around further, I found another large opening in the outcrop on the right side, hiding behind a scraggly shrub trying to make a home in rock. The thrill of collecting is till there! These cavities were lined with pseudomorphs that were up to about 2 inches long (actually further inside, they were up to 3 inches), much larger than most of them on the scattered pieces found on the surface. I started breaking rock to collect the specimens, and soon learned that these two openings were on the same crystal-lined tube. It was 5 feet long and up to 20 inches across. I spent the rest of the day working this cavity, which produced some very fine specimens with pseudomorphs up to 3 inches long and clusters of large crystals up to a foot across with crystals stacked 5 inches high.

Next, the investigation and claim staking.