PHENAKITE: LAZARD CAHN AND WILLARD WULFF

 

High altitude gem collecting on Mt. Antero.

In a recent Post (Dec. 19, 2018) I noted that Edwin Over was a Charter Member of the Colorado Springs Mineralogical Society, one of the country’s oldest rock and mineral societies dating back to inception in 1936.  Mr. Over was a mineral collector of some fame but evidently was not recognizable by many.  It seems as Ed preferred to spend his time in the field collecting as a “lone wolf” (Wilson, 2018) while avoiding the lights and glamor of the cities and auctions.  His best-known field collaboration was with Art Montgomery, a productive union that lasted from ~1934-1941 (see Dec. 19 Post).  One of their collecting localities was on Mt. Antero in Chaffee County, Colorado, in the Sawatch Range near Buena Vista.  The Mt. Antero-Mt. White localities, first discovered in the mid-1880s, are perhaps the highest (elevation) gem collecting sites in the U.S. at nearly 14,000 feet and are “most famous” for aquamarine (blue beryl, Be₃Al₂Si₆O₈, with a chromophore of Fe++ or ferrous iron).  Pearl (1972) noted that Over maintained a camp “near/on” Mt. Antero and collected in summers 1928, 1931, 1932, 1933, 1938, 1951, and 1953; the 1938 expedition was spent with Montgomery. Other than the beryl, the Mt Antero sites have produced beautiful specimens of smoky and clear quartz, various feldspars, muscovite, monazite, fluorite, bertrandite, phenakite and others.  Check out the newsletter of the Colorado Mineral Society for additional information: http://www.coloradomineralsociety.org/newsletters/March2014.pdf  

 

Prospecting for aquamarine on Mt. Antero.

When I first moved to Colorado and started changing my collecting interests from fossils to minerals, I became intrigued with Mt. Antero and decided that would be my first 14er and perhaps even an aquamarine would show up.  I was also sort of fascinated by the mineral phenakite, as in what kind of mineral is that creature, and is it spelled with a “k” or “c” (k is correct). It turns out that CSMS was sponsoring a collecting field trip to the aquamarine sites and so off I went a few days early to secure a camp site, check out the area, and make the trek to the summit ON FOOT.  No cheating for me since I wanted the experience of hiking; however, on the day of collecting I was able to drive an ATV to the main sites at ~13,500 feet and wander all over Antero, Mt. White, Carbonate Peak, and a few other high points. I was able to pick up a few small broken crystals of aquamarine, some terminated smoky and crystal quartz crystals, and a few non-colored beryl crystals. 

On a subsequent trip I located a couple of terminated quartz crystals with a few much smaller, gemmy, crystals attached to the quartz.  Without magnification I simply wrote off these smaller crystals as quartz (phenakite comes from the Greek phenakos meaning deceiver since it “looks like quartz” :), or maybe even clear topaz.  Upon returning home and taking a closer look under a binoc scope, and browsing photos in MinDat, I guessed/identified phenakite as the mystery mineral.  Now, as an old softrocker and paleo person from the plains, I didn’t have the slightest idea what phenakite was or is.  This was early in my career as a mineral collector and we certainly did not have phenakite in Kansas!  Probably not even in the Mineralogy class collection drawers!

Phenakite crystal attached to quartz.  Width of crystal ~3 mm.

Phenakite crystal attached to quartz.  Length of crystal ~3 mm.

Phenakite crystal (cube like) attached to quartz.  Width of crystal ~2 mm.

Phenakite is a beryllium silicate [Be₂SiO₄] that is present in the beryllium-rich granite pegmatite emplaced on Mt. Antero.  Other beryllium minerals at Mt. Antero include topaz and bertrandite (beryllium silicate hydroxide).   Chrysoberyl (see Post July 22, 2016), herderite (see Post August 24, 2018) and pezzottaite (see Post April 29, 2018) are other lithium minerals that have caught my eye.

It is difficult to describe phenakite other than saying keep a sharp eye if prospecting in a lithium rich pegmatite or high temperature metamorphic rocks.  Most crystals are small but some range up to several inches in length (rare). One very confusing identification facet is their habit (Trigonal Crystal System), ranging from prismatic (long) to tabular to modified and/or flattened rhombohedrons.  Crystals are often clear and gemmy; however, they may take on a white to pale yellow color.  The gemmy crystals ate transparent while white crystals are more translucent. They have a vitreous or shiny luster and are quite hard at nearly 8.0 (Mohs). Specimens are quite brittle and break with a conchoidal fracture.  The crystals from Mount Antero are generally small and attached to quartz crystals and seem to be modified rhombohedrons.  However, individual and unattached crystals are found by the dedicated aquamarine hunters and if large enough are faceted and bring a healthy price as gemstones. At other localities phenakite is massive or granular---and really tough to identify.

Unattached phenakite crystal.  Width ~ 8mm.

As noted several times, I am far from a mineralogist and have my difficulties with crystallography, some identifications and descriptions.  If you really want to learn about phenakite check out my colleague Bob Carnein’s article in the September 2015 issue of the Lake George Gem and Mineral Club.  It will make you weep with joy—if you are interested in phenakite!

Prismatic terminated phenakite crystal, length ~4 mm, embedded on crystals of colorless fluorite.  Mass attached to quartz not shown on photo. The Cahn-Wulff specimen.

The real reason that I decided to write this little blurb is the historical significance of one specimen I purchased at an estate sale.  Traveling back to 1936 and the formation of CSMS I find that three of the Charter Members were Lazard Cahn (see Post Sept. 17, 2015)), Edwin Over (see Post December 19, 2018) and Willard Wulff (see Post July 28, 2016).  The phenakite crystal I have is a micromount owned by Lazard  Cahn (d. 1940) and then traded/sold to Willard Wulff.  I can only dream that Cahn acquired the specimen from Ed Over, then passed it on to Wulff, then to his daughter, and it now resides in my small collection.  Now that would be a story!

Go out and chase your dreams no matter how crazy it looks.

                               Shanice Williams

REFERENCES CITED 

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Pearl, R. M., 1972, Colorado Gem Trails and Mineral Guide: Swallow Press, Ohio University Press, Athens.

Wilson, Wendell E., 2018, Mineralogical Record Biographical archive: www.mineralogicalrecord.com.