Quartz after fluorite from Colorado / USA
reported by Martin Gruell
I’m collecting minerals since more than 3 decades, since a couple of years I’ve set my focus on Fluorite. So most times I see a Fluorite specimen I know the locality at the first look or at least I have an idea where it might come from. So things I never saw before will get my full attention. In 2012 I saw a Quartz after Fluorite specimen on a seller-page.
I never saw it before, never heard about the locality. The specimen was not good enough for my collection, but I asked myself, if there could be better material from this particular locality. I did some internet-research and found – nothing.
Finally I contacted the seller who offered this material. He told me that he didn´t own any better specimen, but he gave me the email-address of the guy who discovered this stuff. I contacted him and got an answer. He was very happy that someone appreciated his self-selected samples and gave me lot of information. During months we developed an email-friendship (he is also a Fluorite-nerd). Finally he sold me 4 specimens from his collection and 2 other, not so good samples.
First of all a few information about this find: the discovery was in 1985. The Genoa-prospect (I attached a locality photo of the area) is under the main route (graveled) that was a state highway and now a county road and is the main access to the Alpine Loop Scenic Byway. The mining company owned it back then and didn't mind us collecting. The Mayflower Mill is within 200 yards of the Genoa and was an operating mill for the famous Sunnyside gold mine. The claim was sold in the mid 2000's and posted very threateningly.
The specimens were found in a vug that was about 9 feet high, 4 feet wide and probably 15 feet long. One side was covered with these epimorphs. They were coated with black MnO2 and cleaned with oxalic acid.
A side note. If you ever saw the old Jimmy Stewart movie titled "Night Passage", it was filmed in the Silverton area. There is one scene where the bad guys are shooting at Jimmy Stewart and he's shooting back from an old mining structure with bullets zinging off the tram buckets. That is the Mayflower Mill and he is within 200 yards of the vug I’m talking about. He is standing roughly at the Genoa vein.
San Juan County (Silverton) is the only county in the U.S. that does not have one arable acre, mountains all over the place. It has more peaks above 13,000' than any other U.S. county and the lowest elevation in the county is well above 8,000'. The average elevation is well above 10,000'. The mineral deposits are related to the San Juan Caldera which Silverton occupies the bottom of. There are huge quartz veins running everywhere, some over 100' wide. Many of the veins occupy ring and radial faults that formed when that 19,000' volcano collapsed in a brief catastrophic event to form the caldera. There were at least 15 of these stratovolcanoes that collapsed into calderas that formed part of the range. About 27 million years ago. The largest eruption in the earth's history in terms of volume of emissions was the La Garita Caldera (east of Silverton). It was 1,000 times larger than the famous Yellowstone eruption.
Of interest to you is that the San Juans are often called the American Alps because many say they are the U.S. range that most closely resembles that European range. All these informations and also the locality-photo are from my friend Mark in Colorado, who was one of the discoverers.
To give you an idea of this crazy material here some photos of a few specimens.
Quartz psm Fluorite & Baryte 168 x 129 x 78 mm.
Specimen features Quartz on Fluorite octahedrons to 5.3 cm. Quartz on Barite crystals to 3+ cm. This epimorph has very good relief with quartz on both fluorite octahedrons and Barite crystals standing free. A couple of crystals are not fully encrusted and are visible in these photos. At the lower base you can see the matrix consisting of green Fluorite. The specimen is in excellent condition, even on all these tiny quartz crystals I could´t find damage. The main crystal is very exposed and the assemble is very 3-dimensional. I showed 2 photos in different angles and also 2 close-ups.
As you can see on the close-up photo – many crystals are hollow inside, only the Quartz crystals exist, Fluorite is gone. This specimen features the most 3-dimensional assemble, so it should be shown here.
Now let me show you the craziest specimen I got from this discovery:
Quartz epimorph after Fluorite with Baryte 152 x 141 x 54mm
This one shows the most interesting pseudomorphosis. The Fluorite is completely gone, only fragile crusts of hollow Quartz exists. All other pieces show green Fluorite matrix, but also the matrix is hollow and covered by Quartz. A second generation of Fluorite was grown and this is emimorph, also. So, it’s the same genesis, but 2 layers – Quartz after Fluorite on Quartz after Fluorite, absolutely crazy.
Finally I have to show the largest crystal – I gave this specimen to my dear friend Robert Brandstetter, who is also focused on Fluorite and owns a superb Fluorite collection. This photo is done by Robert, specimen is about 12 x 8,5 cm and the main crystal is about 5 cm across.
I always enjoy seeing something completely different, something unknown so far, that’s the exciting, amazing thing – the thrill of collecting minerals!