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Monday, March 7, 2022

TUCSON 2022 MINERAL CITY: CINNABAR AND GIBBSITE

In my last Post on the Tucson Mineral City Shows I focused on Shannon Family Minerals.  Today I want to point out some of the other selling venues in Mineral City.  In fact, there are several shops that are officially part of Mineral City; however, there are others that are located in the Mineral City area but do not seem affiliated with Mineral City! For example, Barlows Gems have their own permanent location on Lester Street immediately west of “official” Mineral City.  Named the The Rock Yard, this year Barlows had an amazing selection of chrysocolla (hydrated copper silicate) collected from the Bagdad Mine, Eureka Mining District, Yavapai County, Arizona. A beautiful sky-blue color, large pieces from the mineare no longer available (according to a salesperson).

 

The Rock Yard in front of Barlows retail store.


Polished blue chalcedony in specimen trays.


A very large (?24 inches) polished chalcedony specimen.

Dennis Beals, a dealer in specimens from Mexico, moved from the downtown hotel district to Mineral City.  Dennis is from the Denver area and a regular in the Colorado show circuit.  As usual, he regaled me with exciting yarns about collecting trips south of the border.  I was impressed with a specimen of calcite with cinnabar collected from the Cocineros Mine in the Santa Eulalia District, Chihuahua, Mexico, so plunked down my monthly allowance. I can’t find out much information about the mine except that it has produced mercury—how much?  When? 


Cinnabar and calcite, Cocineros Mine.  Width FOV ~1.6 cm.
 

   
Don't drink the tap water in rural Mexico so the next best choice is mescal or tequila!






Vendor banners are the big rage.

I spent about three days wandering around the shops in Mineral City and viewed a large number of interesting and beautiful specimens.  Wendel Minerals had a nice case of varied minerals and a nifty specimen of gypsum collected from the Cavnic Mine in Romania.


Wendy’s Minerals had a very nice selection of blue gibbsite collected from the Hongsheke bauxite deposit, Yanshan County, Wenshan, Yunnan, China. I could not afford the $250-$300 specimens but was able to purchase a nice thumbnail. Gibbsite is an aluminum hydroxide [Al(OH)3] and is one of the three major minerals that make up the rock bauxite, the others being the aluminum hydroxide minerals diaspore and boehmite, plus goethite and hematite (both iron oxides), kaolinite (an aluminum clay), and perhaps a small amount of the titanium minerals anatase and ilmenite.  Actually, bauxite is not a very attractive rock and is usually tan or reddish brown in color with a very dull luster. The formation of bauxite is a quite complex process and is usually classified into two types: 1) carbonate bauxites formed by lateritic weathering of limestone and dolomites leaving behind aluminum rich clays; and 2) the more common lateritic bauxite where lateritic weathering attacks aluminum rich igneous rocks and clays.  In this process there is dissolution of the aluminum-rich clay mineral [Al2(OH)4Si2O5] kaolinite, where silica is removed, and gibbsite is formed. The problem I have is trying to identify gibbsite in specimens of bauxite (usually 40% to 60%) is that most of the bauxite I have collected in Arkansas, or have seen from other locations, is that nondescript tan to reddish brown color with the component minerals seemingly “mixed up”.  



Pisolitic bauxite specimen from Pulaski County, Arkansas collected late 1960’s. Width ~6.5 cm.

Isolated specimens of gibbsite are found in a variety of colors from white, gray, green, reddish white, blue, and non-colored (clear). The latter variety has a vitreous to sub-vitreous luster, is transparent to translucent, and often forms prismatic Monoclinic crystals.  The colored and massive material (from impurities) have lusters ranging from pearly to earthy/dull. There are some specimens, like mine, that appear nodular but under magnification one can observe vitreous to subvitreous lightly colored (blue in this case), translucent, crystals and nodules. 

w
Gibbsite nodules and crystals.  Width FOV ~1.6 cm.

Photomicrograph of above.

The atomic structure of gibbsite is composed of octahedra (an aluminum ion bonded to six hydroxide groups) that are loosely stacked and weakly bonded; therefore, gibbsite is quite soft (~2.5 Mohs). Interesting, the soft gibbsite atomic structure is identical to the structure of very hard [9 Mohs] corundum.  The difference is that oxygen replaces hydroxide in the chemical make composition [Al2O3] and therefore the stacking arrangement of octahedra is well bonded.

One of the nagging questions that I have about gibbsite is---what causes the blue color in some specimens?  I have been unable to locate an answer.  Could the color be similar to blue corundum where impurities of iron and titanium produce several shades of blue sapphire? Or perhaps impurities of iron in the mineral results in the reduction of ferrous iron (3+) to ferric iron (2+) and perhaps the latter form is blue (I am way above my pay grade here, but this guess was based upon a blue color known a ferric blue or even Prussian Blue.  Far out of my league). One of life’s persistent questions.

As for the location of blue gibbsite, China has a number of bauxite deposits, and hence large mines, in Yunnan Province—all seem to have a similar origin: 1) weathering and accumulation of aluminum bearing minerals from “basement rising” rocks; 2) desilication and laterization of the aluminum bearing minerals; and 3) aluminum clay enrichment (Shi and others, 2007).  Since gibbsite is an important constituent of bauxite it evidently is common, or at least collectible, in these mines.

 

REFERENCES CITED

Shi, Zhu-huan, Dong, Jia-long,Yang, Song, 2007: https://en.cnki.com.cn/Article_en/CJFDTOTAL-KCYD200703012.htm



Friday, February 25, 2022

MINERAL CITY AT TUCSON 2022: Zálesíite AND Spadaite

 

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Tucson 2022 has completed its stay in the “Old Pueblo” and featured tens of thousands of mineral and other items to ogle at, or perhaps even purchase.  The Tucson Gem and Mineral Show® completed its 67th version in the second week of February and incorporated material from the cancelled 2021 event (Fluorescent Minerals) with the original 2022 theme (The Apatite Supergroup).  More information on this “main show” will come in a later post.

The “main show” is sponsored by the Tucson Gem and Mineral Society and is restricted to the one show in the Convention Center.  However, there are numerous other events scattered around the city in motels, big tents, little tents, gravel parking lots, permanent buildings, and the beds of pickups.  At one time most of these ancillary events started two weeks before the last day of the “main show.”  However, since these shows are self-regulated, they now start and close on their own schedules, and this year several events started on various dates in January.


The largest of these ancillary shows is the Mineral City Show located north of the Tucson City Centre along Oracle Road.  According to Graham Sutton the idea of forming/building Mineral City was conceived around 2018 when he asked several dealers if they were interested in establishing permanent showrooms for their collections.  Today, after several setbacks mostly concerned with Covid, Mineral City has constructed several permanent buildings and remodeled others and is anchored, at least by people who remember, the old La Fuente eating establishment.  The so-called warehouses are subdivided into different sizes of rooms that serve as selling venues, offices, and in the off season as storage areas.  The selling venues are often furnished with fantastic glass display cases, tables for specimens, overstuffed chairs for resting and visiting; the dealers are mostly middle to high end.  There is also a cantina and snack area snuggled in.  I counted 121 different selling establishments with room for perhaps a few more in future years.

The Mineral City concept is an interesting experiment!  In visiting with some dealers, I got the idea that perhaps some stores would have selling events scattered thru the year, perhaps before Christmas as an example.  I also heard “gossip” that the only people at the 2022 event were collectors and the “general public” and visitors did not show up.  I attended Mineral City on four different days and the traffic thru the selling areas was light (at least in my opinion) and one long time dealer told me that it was his worst Tucson selling event—ever. My biggest concern for the event is a lack of parking.  Few gravel lots are available and parking on curb-less, pothole filled, roads is tough, at best.  Handicapped parking is sparse.  However, I wish Mineral City the best.

My favorite dealer in the Tucson shows, Mike Shannon of Shannon Family Minerals, was located in Mineral City and occupied a large room packed full of flats filled with a variety of minerals with reasonable prices (great for a frugal collector like me).  It took me several hours for a cursory search of the flats; however, I did come up with several goodies, especially from the collection he purchased from Mineralogical Research Company.  





 
Minerals for sale at Shannon Family Minerals.

One of my new specimens is from a favorite Utah collecting site, Gold Hill, an old mining community located south of the bi-state town of Wendover, Nevada/Utah, that was mined for gold, copper, zinc, lead, arsenic, and tungsten from the mid to late 1800s until the late 1940s.  The peak activity was in the early 1900s when a spur railroad reached the area in 1917.  There was only sporadic mining after World War I.

Gold Hill or the Clifton District, contains numerous mines, including an open pit, and is located near the northwest end of the Deep Creek Mountains, perhaps Utah’s most isolated and unknown mountain range.   Peaks do reach 12,000 feet—Ibapah Peak at 12,087 and Haystack at 12,020.  The Deeps are the major topographic feature in western Utah.  The range has a Precambrian core surrounded by Paleozoic sedimentary rocks with later Mesozoic intrusions—mostly quartz monzonite and granite/granodiorite, and later Tertiary volcanics. 

I have described a number of minerals [in this Blog] from the Gold Hill District and refer readers to the Post of January 3, 2015, where the mineralization is described in greater detail. Today I want to add the mineral zálesíite [CaCu6(A2O4)2(AsO3OH)6-3H2O] to my list. This somewhat rare hydrated hydrous calcium copper arsenate was not named and described until the end of the 20th Century (Sejkora and others, 1999) from the Czech Republic, and noted from Gold Hill soon after (Adams. 2005). Previously, known (at times) specimens of zálesíite were called agardite-Ca or REE-free agardite. Agardite is a REE-dominant hydrated hydrous copper arsenate that is a member of the Mixite Group and is in a solid solution relationship with zálesíite (Sejkora and others, 1999).  The Mixite Group, according to MinDat.org, is a “group of chemically complex, visually indistinguishable arsenates and phosphates.”  I have described, in past postings, mixite from the Gold Hill and Tintic areas in Utah.

Photomicrograph, best I could do, of sprays of
zálesíite ~1 mm in diameter with green
spheres of conichalcite [CaCu(AsO4)(OH)].  With a binoc scope the sprays appear to be pale green in color.
A submillimeter spray of zálesíite with ~2 mm spheres of conichalcite.

Zálesíite is the calcium- and arsenate- dominant member of the Mixite Group and forms from chalcopyrite and arsenides in conditions of supergene zone in-situ weathering (Sejkora and others,  1999).  The crystals of zálesíite are: acicular and needle like, very minute (usually less than half a millimeter in length), often forming radiating small masses, generally transparent, very soft (~2-3, Mohs), having a semi vitreous to silky luster, and are said to be pale green in color.  However, crystals on the specimen I have are more “pale white” in color and match the photos on Mindat.org of other specimens from Gold Hill.  In reality, I am depending on the identification of the Mineralogical Research Company since Mindat.org states, members of the Mixite Group are “often only unambiguously identifiable by quantitative electron microprobe analysis.”  This is sort of above my pay grade!

And speaking of Gold Hill----I also picked up another mineral from that locality (collected from Alvarado Mine) at the Show: spadaite.  Well maybe a mineral since Mindat.org offers this opinion: “questionable species with unknown structure.  No x-ray pattern has been published in the literature.” However, spadaite has been around for a long time since its initial description in 1843 from Italy (von Kobell).

The magnesium silicate spadaite [MgSio2(OH)2-H2O(?)] is a nondescript, colorless to cream to pinkish, soft (2.0-2.5 Mohs), amorphous, dull, mineral.  It forms massive (no visible crystal structure) “hunks” with no visible crystal structure that sometimes are felted and shreddy, or sometimes dense porcelain-like. Spadaite seems limited to areas of skarn rocks (AKA tactite) where contact metamorphism and metasomatism affects carbonate rocks. At its type locality in Italy spadaite is associated with leucite-bearing basalt, in Germany with amygdular diabase.

Spadaite was first noted from the Gold Hill area by Schaller and Nolan (1931) as they prepared for Nolan’s seminal paper on Gold Hill (1935): “During the survey of the Gold Hill quadrangle in west central Utah, several specimens of an unusual type of gold ore were collected by one of us (T. B. N.). On microscopic examination these specimens were found to contain considerable quantities of a fine grained shreddy mineral which could be referred only to the very rare mineral spadaite on the basis of optical and chemical.”  He noted that spadaite only occurs in the ore shoots and is associated wit the siliceous silicates wollastonite, garnet, diopside, and others.  He believed that spadaite preferentially replaced wollastonite but was definitely younger than the original calcsilicate, contact metamorphic mineral (CaCO3).  A follow-up paper by University of Utah graduate student H. El-Shatoury and his advisor James Whelan (1970) briefly noted Nolan’s description of spadaite but preferred to use massive-bladed wollastonite for the major skarn mineral.

A pretty ugly piece of dirty white, massive spadaite that has replaced wollstanite in a skarn deposit.

Today one does not see many specimens of spadaite on the market and Mindat.org shows only 8 photos, half of which are from the Alvarado Mine at Gold Hill.  So, I would say that it is not an attractive nor popular or common mineral.

                     REFERENCES CITED

Adams, P.M. (2005): Zalesiite from the Gold Hill Mine, Toole County, Utah: Mineral News, v. 21, no. 8.

Nolan, T.B., 1935, The Gold Hill Mining District, Utah: USGS Professional Paper 177

Schaller, W.T. and T.B. Nolan, 1931, An occurrence of spadaite at Gold Hill, Utah: American Mineralogist v. 16.

Sejkora, J., T. Řídkošil, and V. Šrein, V.,1999, Zálesíite, a new mineral of the mixite group, from Zálesí, Rychlebské hory Mts., Czech Republic: Neues Jahrbuch für Mineralogie, Abhandlungen v.175.

Shatoury, E.L. and J.H. Whelan,1970, Mineralization in the Gold Hill Mining District, Tooele County, Utah: Utah Geological and Mining Survey Bulletin 83.

von Kobell, F.,1843, Ueber den Spadaït, eine neue Mineralspecies, und über den Wollastonit von Capo di bove: Journal für Praktische Chemie v. 30.

 

                                                                                                               

 

Monday, January 24, 2022

29378 Ua Controller 220/240 Volt 3N-2016-W50-1 (CB3))

 

BLACK HILLS MINERAL

Collected Ross Mine

Unattractive graftonite

Is it a keeper?

I am always on the lookout for phosphate minerals and have documented several in this Blog.  The Black Hills of South Dakota is among my favorite places, both to collect, and just to drive around and enjoy the scenery.  Stay away from Mt. Rushmore and Deadwood and the causal collector/observer may be able to mosey along tens of miles of back country roads free of traffic and peppered with nice roadcuts.  Most of the interesting phosphates come from the Precambrian Harney Peak Granite and associated pegmatites. Although mines, pits, and other diggings seem scattered everywhere, many are on private lands and/or are under claim so permission to explore off road is necessary.  Often the desirable and collectable phosphates are secondary minerals and microscopic, so a loupe in the field and a good scope at home is necessary to enjoy their beauty.

During this winter break (whatever that means since being “retired” indicates my break is ongoing) I have been doing some specimen sorting and came across a Black Hills box containing a few unspectacular specimens. Some were collected back in the middle 1960s when wandering and the freedom to collect minerals were more common than today.  So, I decided to bite the proverbial bullet, check labels with identifications and  locations, and get them into the correct South Dakota drawer.

It turns out that all located specimens are massive phosphate minerals. However, my major problem with these “rather ugly” phosphates is their difficulty in identification.  I probably should state it is “my difficulty in identifying these specimens with simple physical properties.”  I am certain that my colleague Tom Loomis up at Dakota Matrix in Rapid City could take one peek with a loupe and spit out a name! It is just tough for me to make that final? identification.

One of these creatures is labeled graftonite collected from the Ross Mine in Custer County.  I will stick with that identification from 50+ years ago and but it could also be from the nearby Bull Moose Mine. As an aspiring stratigrapher/ paleontologist I was not always accurate with collecting information on unspectacular massive and dark colored minerals.  But I did note it was from the Ross.

Graftonite is a ferrous iron phosphate [Fe2+Fe2+2(PO4)2 ]—maybe.  However, the IMA distinguishes between graftonite (Fe), graftonite (Ca) where calcium substitutes for some of the iron, and graftonite (Mn) where manganese replaces some of the iron.  In the chemical formula just replace the second Fe with either Mn or Ca.  In fact, the Handbook of Mineralogy defines graftonite as [(Fe2+, Mn2+,Ca)3(PO4)2]. In reality, most graftonite probably contains some iron, calcium and manganese.  Unfortunately, my “lab” does not contain any electronic gizmos that could produce the percentage of the graftonite cations!

Graftonite is some shade of brown to reddish brown (depending on the amount of iron), depending on light conditions it may appear less-than-vitreous to greasy, has a white streak (mostly), and a hardness of ~5.0 (Mohs). It rarely exhibits crystals and, as a primary phosphate, is usually associated with triphylite [LiFe2+PO4] in complex granite pegmatites. Graftonite is not a really attractive mineral and most likely would be missed on a routine collecting trip.

Brownish graftonite ~3.0 cm x 1.4 cm.  A cross sectional view (in one of my lost/misplaced files) would show bands of graftonite alternating with triphylite.

Not to be left out of the “not-too-attractive” mineral category is griphite, an extremely complex phosphate: Na4Li2(Mn2+,Fe2+,Mg)19Al8(PO4)24(F,OH)8.  In fact, so chemically complex that it was named for the Ancient Greek term for puzzle:  γρῖφος (grîphos). Griphite is another brown to yellowish brown to blackish brown phosphate; the exact color depends upon the mix of cations. It is brittle, has a vitreous to resinous luster, a hardness of 5+ and is translucent in thin sections: sort of non-descript, dark colored, primary phosphate!

Dark brownish-black, massive, resinous griphite. Maximum dimension ~3.0 cm.

The specimen I acquired several years ago has an older typewritten label (glued on the box)indicating it was collected in Custer County in the southern Hills.  However, that is probably wrong as almost all griphite specimens in the Hills (and in the world) come from either the Everly Mine (Type Locality) two miles east of Keystone or, to a lesser extent, the Sitting Bull pegmatite one mile northwest of Keystone (both in Pennington County). In fact, my “Custer” was crossed out on my label and Everly was penciled in. That seems reasonable since Roberts and Rapp (1965) noted that “griphite occurs in dark brown resinous masses… in granitic pegmatite at the Riverton lode (Everly Mine) near Harney City two miles east of Keystone”. As Robert Lavinsky noted on MinDat, not pretty to look at but is a rare species.

And from the same collector as the previously described griphite is a specimen of lithiophilite from the Dan Patch Mine in Custer County-well maybe?  First of all, the Dan Patch is in Pennington County ~ one mile west of Keystone near Mt. Rushmore.  Feldspar and beryllium were mined from a pipe-like pegmatite body. Second, lithiophilite is unreported from the Dan Patch although triphylite is known. My guess is that the Dan Patch Mine is correct for the collecting locality since Roberts and Rapp (1965) noted, “ cleavable masses of greenish-gray unaltered triphylite up to 8 feet by 3 feet in size occur in great abundance at the Dan Patch Mine.” My specimen is a gray to greenish-gray color with a hardness of ~4.0 (Mohs); lithiophilite is usually some shade of brown or salmon in color. The luster is greasy to resinous, it is cleavable, brittle and has a colorless to off-white streak.  I am sticking with triphylite as defined by Roberts and Rapp (1965). 

Greenish gray massive triphylite ~3.1 cm x 2.6 cm.

What about the identification as the primary phosphate lithiophilite? Probably wrong but an easy mistake to make—triphylite (also primary), the lithium-iron phosphate [LiFe2+PO4], and lithiophilite, the lithium-manganese phosphate [LiMn2+PO4] are end members of an isomorphous solid solution series. I certainly have difficulty identifying either mineral and like many other rockhounds, refer to either/or as triphylite-lithiophilite. Throw in the alteration minerals sicklerite [Li(Mn3+Fe2+)PO4] and ferrisicklerite [Li(Fe3+Fe2+)PO4] and I am really confused!

But wait, there is more! Heterosite [(Fe3+,Mn3+(PO4)] and purpurite [Mn3+(PO4)] are secondary phosphate minerals that are the result of the oxidation of triphylite-lithiophilite and are themselves in a solid solution series and difficult to distinguish between. In both heterosite and purpurite the lithium is leached from the parent minerals. MinDat noted “that intermediate alteration products are part of a continuous process of alteration: ferrisicklerite and sicklerite are intermediate between the unoxidized and unleached parent minerals and the completely leached and appropriately oxidized end-products, but may not be valid species.”  I have concluded that Tom Loomis, Mr. Phosphate, of Dakota Matrix may be the only rockhound/mineralogist who can properly identify these phosphate minerals of the Black Hills.

There are also light colored, primary phosphate minerals in the pegmatites of the Black Hills.  For example, two minerals that confuse me (not hard to do) are the fluorophosphate amblygonite and the hydroxyl phosphate montebrasite.  Both are lithium aluminum phosphates that lack iron and manganese and are in a solid solution relationship:  LiAl(PO4)F—LiAl(PO4)(OH). Although Roberts and Rapp (1965) list a large number of collecting localities for amblygonite and only a few for montebrasite, they further state, “montebrasite, together with amblygonite, has been mined extensively in the state [SD] as an important lithium ore.  Upon further investigation, many of the reported occurrences of amblygonite in this area [Black Hills] will in all probability, prove to be montebrasite.”  In addition, MinDat noted, “montebrasite is, by far, the most common member of the group.  Amblygonite is scarce.” However, MinDat localities for amblygonite are far more numerous than montebrasite! It appears that additional identifications are needed to shift many of the amblygonite localities over to montebrasite.

Both montebrasite and amblygonite are similar in appearance: massive, white streak with a color of white, milk white, colorless, pale yellow; mostly resinous to greasy luster maybe sub-vitreous; hardness of ~5.5-6.0 (Mohs); will cleave; translucent to transparent.  Montebrasite may have a pink or brown tint.  Amblygonite may be beige, salmon, light green, light blue in color.

I have only seen the massive to white specimens that could easily be mistaken for milky quartz and not worth a “bend over” to pick up.  However, quartz is slightly harder than either, has a lighter heft (specific gravity of ~2.6 vs. 3.05), and a vitreous luster; all hard to distinguish “in the dirt” while sorting rapidly. Although I have never seen crystals, “montebrasite forms attractive, colourless, bright yellow-green, sometimes blue, pink and pale brown, equant to short-prismatic crystals” that may be faceted (Gemdat.org).  Amblygonite crystals may be faceted but are rare.  Care must be taken with either faceted gem due to the low hardness and poor toughness (Gemdat.org).

Snow white montebrasite.  Length ~3.3 cm.
 

The specimen I picked up many years ago simply said “amblygonite, Keystone District, Black Hills.” However, I believe the correct ID is montebrasite from one of many mines in the District.  I base this decision on: 1) previous discussions about the rarity of amblygonite; 2) most/many examples of amblygonite have some shade of color; my specimen is snow white; 3) an identical looking specimen of montebrasite is shown in MinDat photos as coming from the Keystone Mining District.

So, that is my take on some of the primary phosphate minerals from the Black Hills.  They are not recent finds as I located them stuck away in one of my many boxes that I always intended to open up and be surprised.  And that I was, and believe me, for an ole soft rocker I learned much.  That is what life is all about at my age---keep on truckin'!

The love of learning, the sequestered nooks,
And all the sweet serenity of books

Henry Wadsworth Longfellow

REFERENCES CITED

Roberts, W.L. and G. Rapp. Jr., 1965, Mineralogy of the Black Hills: South Dakota School of Mines and Technology, Bulletin Number 18.

All MinDat and GemDat references were accessed in January 2022.