DUFTITE: A NICE GREEN ARSENATE

Got to love those Arizona sunsets!  West face of Superstition Mountains near Apache Junction.

I can always rely on my friend, Mr. Rockhounding the Rockies, to supply me with some rather odd and sometimes unique crystals. Those who read his Blog (www.rockhoundingkw.blogspot.com) know this prospector is interested in “big” crystals of amazonite and smoky quartz.  He might stoop to collect some brightly colored fluorite or some nifty goethite but his heart and soul are dedicated to those “really” big pegmatite crystals near Lake George, Colorado.  Someday I hope to transport him to the Black Hills of South Dakota to check out spodumene and feldspar crystals that measure in tens of feet!  In the meantime, I continue to accept what scrapes he throws my way---I just posted a new photo of “zinnwaldite” collected near Lake George (Blog 11/12/13).  Mr. Rockhounding has never collected in Mexico but recently he tossed me some microcrystals of really curious arsenates, including duftite, that I believe came from the Ojuela Mine, Mapimi, Durango, Mexico.  I eagerly accepted since I am a sucker for bright-colored minerals. Got to love those Arizona sunsets!  West face of Superstition Mountains near Apache Junction.

Dufitite [PbCu(AsO₄)(OH)] is a lead copper hydroxyl arsenate found as a secondary mineral in the oxidized zone of sulfide ore deposits.  The arsenates contain a suite of beautiful and often confusing (to identify) minerals.  Adamite is perhaps the best known of the group but others include cornwallite, erythrite, olivenite, legrandite, chalcophyllite, scorodite, etc.  In textbooks, the arsenates (contains the AsO₄ radical) are often grouped together with the phosphates (PO₄ radical) and the vanadanates (VO₄ radical) since the radical often can interchange with each other and therefore create new minerals.  All together the three groups form an amazing number and variety of often brightly-colored minerals that are exciting to collect and observe but tough to identify.  It seems best to always carry a microprobe in your back pocket in order to obtain a specific identification!

Green duftite botryoidal duftite on "limonite."  Width of specimen ~3.1 cm.

Green duftite botryoidal duftite on "limonite."  Width of specimen ~2.5 cm.

As stated many times, I am not a mineralogist but do enjoy learning as I muddle through the minerals.  I am familiar with the arsenate and green encrusting mineral conichalcite since it has been found at Gold Hill in western Utah (see Blog posting Dec. 13, 2011).  In fact, duftite and conichalcite [CaCu(AsO₄)(OH)] form a solid solution series with the calcium of conichalcite substituting for the lead of duftite.  And in fact, austinite [CaZn(AsO₄(OH)] is also thrown into the soup with the zinc substituting for the Cu, or parts thereof.  At the type locality of duftite at Tsumeb, Namibia, a detailed 1980 study of the solid solutions in the arsenates found that “things” are not as straightforward as seemed—perhaps the original type duftite is not really “all” duftite: “the specimens are commonly zoned in color and composition. Microprobe analyses and X-ray powder-diffraction studies indicate extensive Cu-Zn and Pb-Ca substitutions, which represent solid solution among conichalcite… austenite… and duftite” (Jambor and others).  Green duftite botryoidal duftite on "limonite."  Width of specimen ~3,3 cm.

Photomicrograph of green botryoidal duftite on "limonite."  Width of width of photo ~1.1 cm.

The Handbook of Mineralogy (www.handbookofmineralogy.com) noted that conichalcite is “an uncommon secondary mineral in the oxidized zone of copper deposits, typically an alteration product of enargite” [copper arsenic sulfide] while duftite is “an uncommon mineral in the oxidized zone of some hydrothermal base-metal deposits.”  So, copper needs to be present in the solution for conichalcite to crystallize while lead must be around for the formation of duftite. 

 

So, what is an ole duffer like me going to call a specimen of green botryoidal crystals?  I don’t have a probe or FTIR or powder x-ray apparatus so must rely on physical appearances!  Yes, I know, that is the first thing instructors in Geology 101 tell students---don’t rely on color.  However, the physical properties of duftite and conichalcite are very, very similar.  I am calling my specimen duftite since: 1) some obscure pencil marks on a small slip of paper provided by the original owner labeled it duftite; 2) it “looks like” photos of duftite displayed on Mindat.org rather than conichalcite; 3) it “looks different” from the specimens of conichalcite in my collection.  That is the best that I can accomplish.  One great “thing” about a personal blog is that the editor easy to please.

As with much of what I write: The more I live, the more I learn. The more I learn, the more I realize, the less I know.  (Michel Legrand).

REFERENCES CITED

Jambor, J.J.. D.R. Owens, and J.E. Dutrizac, 1980, Solid Solution in the Adelite Group of Arsenates: Canadian Mineralogist, v. 18.

CALLAGHANITE; A RARE BLUE CARBONATE

BESIDES BLUE MINERALS ARIZONA HAS SOME FANTASTIC SUNSETS SUCH AS THIS PHOTO NEAR CAVE CREEK.

I have noted before in these postings (especially see August 21, 2012) about my first trip, in 1967, to Salt Lake City, Utah, so that I could attend graduate school.  I was just a small town Kansas kid and came from a high school of 48 students (that is total for all four grades)!  If I misbehaved in school it was likely that my father knew about it before I reached home after the end of classes.  Word seemed to travel rapidly in a small town. The great “things” about this childhood included participating in a variety of sports, getting a pretty fair education (four years of math, science, and English) and being able to spend any free time tromping around the countryside collecting rocks, fishing, camping, and hunting for a mythical cave (see posting July 23, 13). 

I attended the University of South Dakota and completed a MS degree and now was heading west (with a spouse of 5 days) to experience life as a frontiersman (or so I dreamed) and get another degree.  But, upon popping over the Wasatch Mountains and seeing Salt Lake City I was flat-out scared.  Wow, this was a big city (~250 ka) and the University was probably really large (everything is relative to the times).  We had little money but found a small apartment where the rent was $35 every two weeks, and we were off.

At that time the University of Utah followed an “old school” model with  three different and separate departments:  Geology, Geophysics, and Mineralogy; each area had a chair and faculty.  All departments had good faculty members; however, I became quite fond of two in geology—Armand Eardley, a well-respected structural geologist and stratigrapher Lee Stokes (my major adviser).

  

The Utah Geological Survey was intimately associated with the departments and their Associate Director was an economic geologist by the name of Eugene Callaghan.  In 1968 the three departments consolidated into the Department of Geology and Geophysics and Callaghan became the Chair.  In retrospect, I suppose securing an external chair was an appropriate political move that would not “favor” a single department.  At any rate, I was spellbound when listening to Callaghan talk about his past careers and travel spanning most of the world’s continents, especially his stint as chief geologist for Cyprus Mines Corporation, and his field work in 1930’s Nevada. They were fascinating stories.

Over the years since leaving Utah in 1970, I had not really thought much about Dr. Callaghan except when I read an article detailing some of the interesting geology of Cyprus.  Not being a mineralogist, I often had difficulty understanding the complex ore mineralization present on that island! 

This winter, while rummaging through some mineral specimens at a small venue at the Tucson shows, I came across a thumbnail specimen with a smear or two of blue color.  Now, I am a sucker for blue minerals so shelled out a couple of dollars and tucked it away.  Imagine my surprise when I returned home and checked out the “blue specimen” labeled Callaghanite from Nye, County Nevada, and found that the mineral was named after the former department chair at the University of Utah--one of those serendipitous moments. 

 

PHOTOMICROGRAPH OF A CALLAGHANITE VEINLET WITH TINY NODULES OF WHITE DYPINGSITE [Mg₅(CO₃)₄(OH)₂-5H₂O] or HYDROMAGNESITE  [Mg₅(CO₃)₄(OH)₂-5H₂O.  THE NODULES ARE LESS THAN 1 MM IN WIDTH.

INCRUSTATION OF BRIGHT BLUE CALLAGHANITE.  WIDTH OF "BLUE" SECTION ~1.1 CM.

MAGNESITE OR HYDROMAGNESITE (MATRIX) WITH A BLUE INCRUSTATION OF CALLAGHANITE.  WIDTH OF SPECIMEN  ~2.7 CM.

Callaghanite was named by Beck and Burns (1954) and was described as “…small, azure-blue crystals from the working pits of the Gabbs Refractories Inc. Gabbs, Nevada [Nye County] and is…a hydrated basic copper, magnesium, calcium carbonate, Cu₄Mg₄Ca(OH)₁₄(CO₃)₂-2H₂O [now noted as Cu₂Mg₂(CO₃(OH)₆-2H₂O]…The mineral occurs near peridotite dikes intrusive into magnesite and dolomite…part of the Luning formation of Upper Triassic age...At the contact between magnesite and diorite, magnesite has been changed to brucite and diorite has become more basic by assimilation of magnesia. Apophyses of diorite within brucite may be changed completely to serpentine. A thin band of forsterite often marks the boundary between the serpentine and brucite…[Callaghanite] generally is found within this serpentine-forsterite-brucite zone where it occurs as tiny disseminated crystals, as encrustations, and as veinlets. The field relationship of the mineral suggests that it is hydrothermal in origin.”  Beck and Burns  also suggested that the hydrothermal solutions normally would have precipitated azurite but because of the magnesium and calcium in the surrounding rocks, Callaghanite was formed.

Callaghanite is usually reported as being “very rare” and for decades was only known from the type locality.  Beginning in 1988 reports begin to trickle in about rare occurrences in Austria, Germany, Italy, and Oklahoma, USA.  See Mindat.org for references. 

The Deseret News of Salt Lake City, reporting on the death of Dr. Callaghan, reported: his distinguished professional career spanned 62 years and seven continents. He received his B.A. and M.A. in geology from the University of Oregon and a Ph.D. in geology from Columbia University in 1931. From 1928-46, he conducted research and geologic mapping in Utah, Nevada, Massachusetts, Puerto Rico, and South America for the United States Geological Survey. In 1946, he was appointed professor of economic geology at Indiana University.  During 1949-57, Dr. Callaghan directed the New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico. After 1957, he served as international consultant to Haile Mines Corp., DeLiew, Cather & Co., and other firms for which he conducted surveys in Cuba, Mexico, Canada, Turkey, Iran and other countries. From 1958-60, he was chief geologist for Cyprus Mines Corp., conducting studies in Cyprus, Greece, Israel, Arabia, Spain, Portugal and Morocco.  During his retirement (post 1972), Dr. Callaghan continued geologic consulting and attending professional conferences in Ireland, Scotland, Kenya, People's Republic of China, Australia, and Antarctica, among others.

As a summary note, Callaghanite actually was named for Dr. Callaghan’s time as Director of the New Mexico Geological Survey and his work with magnesite.

REFERENCES CITED

Beck, C.W. and J.H. Burns, 1954, Callaghanite, a New Mineral: American Mineralogist, v. 39.