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Minerals (continued from page 2)

 

 Duftite is found at the southeastern prospect.  This mineral has been the most debated species found at Rhyolite Pass.   At first, based on appearance and deposit chemistry, the material was speculated to be bayldonite.  Some initial optical testing disproved this hypothesis however and the general properties and appearance of the mineral along with the initial test data pointed to the species duftite. This identification was further reinforced by an independent analysis by Bill Wise (U.C. Santa Barbara), who also concluded based on SEM-EDS analysis of the chemistry that the mineral was probably duftite.

Later, an analysis was performed by Paul Adams, who performed both SEM-EDS and XRD studies on the mineral.   In the specimens that he tested, Paul observed the presence of vanadium. Taking this into account, along with the XRD data, he concluded that it was very likely that the material was not duftite, but was instead mottramite.

So the question arises, why is this mineral being classified as duftite?  In all truth, the call is subjective.  First of all, the XRD patterns for duftite and mottramite are extremely similar. Secondly, the duftite was found in intimate association with other arsenate species.  Last of all, the material just doesn't resemble mottramite, it looks like duftite.  This is the consensus of the several individuals who have viewed the material.  For the time being then, this material will be classified as duftite. Or perhaps, the material could be classified as either vanadium-bearing duftite, or vanadian duftite.

The material occurs as lustrous grass-green crystals of a bladed habit.  There is a tendency for the crystals to form stacked aggregates.

 

Duftite, SEM photo

Figure 16.  Duftite.  P. Adams SEM photo, R.W. Thomssen specimen.

Figure 17.  Spectral analysis of duftite (specimen originally labeled bayldonite).  P. Adams data

Figure 18.  XRD data for duftite sample.  P. Adams data.

Duftite, Rhyolite Pass

Figure 19. Duftite cluster.  S. Sears specimen and photo.

Duftite, Rhyolite Pass

Figure 20. Duftite, southeastern prospect.  S. Sears specimen and photo.

 

 

 Lavendulan occurs in the vein material from both collecting sites.  It typically forms as light blue, anhedral space fillings near the surface of the vein walls.  A few well formed specimens have been collected which display the characteristic micaceous habit of this species.

 

 

 Malachite occurs quite commonly at the main mining area and the southeastern prospect.  This species forms either as velvety spherules of a dark green color, or as radiating groups of emerald green, acicular crystals.  The tightly packed spherules of this mineral can easily be discriminated from such species as cornwallite by the velvety texture, softness of the material, and effervescence in dilute HCl.

 

Malachite, Rhyolite Pass

Figure 21.  Tufted malachite aggregates with minor brochantite.  S. Sears specimen and photo.

 

 

 Mimetite occurs with moderate frequency at this locality.  Growth textures indicate that it was one of the latter formed species, quite commonly being perched upon the remnants of an earlier mineral growth.  This species tends to form as radiating groups of slender acicular crystals, quite often perched on a pale yellow mat of microcrystalline mimetite.  Less commonly, this mineral forms pseudohexagonal prisms up to several millimeters in size.  The coloration of this species is clear to very pale yellow.

 

 
Figure 22.  Mimetite, Rhyolite Pass.  S. Sears specimen and photo.

Mimetite, Rhyolite Pass

Figure 23.  Pseudohexagonal twin of mimetite, approximately 3mm.  S. Sears specimen and photo.

 

 

 This species was virtually non-existent at the main mining area.  However, in some vein material at the southeastern prospect, it was extremely plentiful.  This species occurs in a variety of well crystallized habits including the fibrous leucochalcite variety.  Several specimens of this mineral were collected with crystals up to a few millimeters in length.  Olivenite from this locality occurs in a variety of colors ranging from a dark green-brown to a light olive green.  The variation in color is probably due to impurities in the crystalline structure.  

 

  Olivenite, Rhyolite Pass Olivenite, Rhyolite Pass
Figures 24 & 25.  Olivenite, Rhyolite Pass.  S. Sears specimens and photos.

Olivenite, Rhyolite Pass

Figure 26.  Sceptered olivenite crystal.  S. Sears specimen and photo.

Leucochalcite, Rhyolite Pass

Figure 27.  Olivenite, leucochalcite variety, with barite.  S. Sears specimen and photo.

 

 

 Pharmacosiderite has been found at both the main mining area and the southeastern prospect.  This species is found quite rarely as cubes up to about 1mm in size.  More often, pharmacosiderite occurs as microcrystalline druses of a yellow color, lining cavities in the matrix.  The color of the larger cubes is typically orange-brown.  Special attention needs to paid to the morphology of these larger crystals.  A few, nearly cubic, iron stained barite crystals were observed that at first, appeared to be pharmacosiderite.  Closer inspection however, revealed the slight rhombohedral geometry.

 

  pharmocosiderite, Rhyolite Pass
Figure 28.  Large pharmacosiderite cubes.  S. Sears specimen and photo.

 

Speculative Mineral Species

 

 Anglesite has been proposed by both Dick Thomssen and Bill Wise.  In one case, the crystals were described as silver-gray in color, underlying possible arseniosiderite.  In another specimen, the crystals are clear prisms.

 

 

Small brown balls, consisting of radiating groups of microcrystals, have been speculated to be the species arseniosiderite.

 

 

 Reports of the occurrence of this species at Rhyolite Pass was the motive for investigation of this site by members of the NCMA.  The basis for this identification was a spectral analysis of the material.  It is the considered opinion of several individuals, that the presence of barium in this initial analysis was most likely due to contamination or substitution of small amounts of barium in the crystalline structure of these specimens.  Barium produces a prominent spectral response for even the slightest content and there is considerable barium present in the vein material from this locality.  Therefore, it is believed that this species is actually pharmacosiderite and not barium pharmacosiderite.

 

 

 Reports of this species also drew the NCMA investigation group to Rhyolite Pass.  However, the group has not verified any specimen of this mineral from the Rhyolite Pass area.  Some material with a chenevixite-like encrustation was observed.  Perhaps this is the material that is being referred to as dussertite.  These specimens were being offered for sale by Mineralogical Research Company.

 

 

 Poorly formed, striated prisms of a steel-gray color, may be enargite.

 

 

 Refer to the description of beudantite.  Some of this material may in fact, be gartrellite.

 

Figure 29. Suspected gartrellite.  S. Sears specimen and photo.

 

 

 Dick Thomssen acquired a single specimen of a bright, crimson red coating on mimetite.  He speculates that this coating is the species minium.

 

 

 Based on initial spectral analyses and morphology, it is suspected that perhaps some of the material presently classified as beudantite, could in fact, be the species segnitite.

 

Acknowledgments

I would like to thank Paul Adams for contributing data from his analyses.  I would also like to thank Bill Wise, Dick Thomssen, Tim Rose, and Mike Kokinos for assistance in species identification and aid in the preparation of this article.  Finally, I would like to thank Sarah Mcguire of the Nevada BLM for providing claims research and historical data.

 

References

FRANCIS, P. (1995) Volcanoes, A planetary perspective.  Oxford University Press, New York, 443 p.

JENSEN, M., (1985) The Majuba Hill Mine, Pershing County, Nevada.  The Mineralogical Record, 16, 57-72.

KOKINOS, M., and WISE, W.S., (1993) Famous mineral localities: the Gold Hill mine, Toole County, Utah.  The Mineralogical Record, 24, 11-22.

ROSS, R.C., (1961) Geology and mineral deposits of Mineral Co., Nevada.  Nevada Bureau of Mines and Geology Bulletin 58.

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