TUCSON: A MASS OF MILLERITE. NICKEL SULFIDE

Instead of worrying about what you cannot control, shift your energy to what you can create.   Roy T. Bennett

This is an interesting time that we are now experiencing, one that is pretty frightening to those that are “most venerable” (over 70) but also for many children and for those who have lost their source of income.  I am a fairly social person so separation from my friends, especially the morning coffee group, has been difficult!  Well not really difficult as that term is reserved for those suffering medical difficulties, for those who are hungry and without shelter, and for our medical workers who are doing a terrific job under not very good conditions.


So, I am pretty much sheltered in place and making the best of it.  I have been madly borrowing e books from our Colorado Springs library and digesting about one per day.  Of course, I have started on a regime of “easy reads”—mostly pulp westerns, especially those authored by Louis L`amour.  As a geologist I love reading, and dreaming about, his vivid descriptions of western landscapes, rocks, and minerals (but not always accurate).  At least once per day I pick up Nathaniel Philbrick’s Mayflower and read a few pages.  I am learning much from this tome but in today’s world I want something light where the winner always kisses the horse, wins the lady, and rides off into the sunset.

Besides reading, I am trying to offer a few more Postings on the Blog; however, this has been a biggly problem.  For the last two weeks my battle has focused on a computer that has been “acting up.”  After hours and hours of uninstalling and reinstalling software and fooling around it finally crashed and burned and I abandoned it when the cursor disappeared.  So it was off to the computer store with the credit card and a plead to the tech people to transfer over as much as possible (although I have all photos and docs saved on external drives).  It took them several hours for the transfer as the old one suffered numerous “freeze ups.”  Then the real fun started as my attempt to restart the digital camera and new software tested my patience.  In addition, due to the pandemic the internet seems “overloaded” and my signal is quite weak so the massive Office suite of software will not load.  However, these malfunctions are minor compared to the medical and economic difficulties around the world.  So, I yell at the computer, but try and remain “happy” and satisfied.  My family and I are well, and I urge readers to take precautions and stay well.


The Tucson shows have been over for seven weeks or so and most local shows and meeting have been cancelled/postponed (The Colorado Mineral and Fossil Spring Show in Denver to May 15-17).  But, I have several miscellaneous specimens dragged home from Tucson so there is much to examine and study. 


A long time ago, at least in Blog time (June 2014), I posted, as part of three articles on nickel, on a really interesting nickel sulfide [NiS] called millerite.  Now millerite is not a rare mineral; however, the collecting localities I described were from Paleozoic carbonates in the Midcontinent Region of the U.S., essentially from Michigan through Kentucky.  And, the millerite crystals are found encased in concretions/geodes (such as the famous Keokuk Geodes).


I am still not certain that a definite answer exists as to the source of the sulfides but Wenz and others (2012) believed the ores of the Mississippi Valley-type Deposits (such as the Viburnum Trend, the New Lead Belt in the Missouri Ozarks) are the result of the introduction of sulfides into lead- and zinc-rich ore fluids that in turn were derived from the 1460 Ma Precambrian basement rocks.  The sulfides may have been derived from local organic- and sulfur-rich carbonate rocks.  Galena (lead) and sphalerite (zinc) are non-complex sulfides and are the stable forms in a low temperature environment (the depositional environment of the Mississippi Valley-type Deposits).  Marcasite and pyrite, common simple sulfides found in the carbonate rocks of the Midwest, may be the result of precipitation from marine waters (I think).

Another thought seems to center around fluid movement from the deep basins present in the Midwest to the rims of the basins during later orogenic events.  In this model the source of the metals is leaching from sedimentary and other rocks (Precambrian basement?) at higher temperatures in the deep basins, and then migrating to shallower levels where they can combine with free sulfide ions, probably resulting from the action of sulfide-reducing bacteria in the shallow rocks (model from Stefano, 2014, discussion on www.Mindat.com). 

Millerite is a fascinating mineral, at least to an old paleontologist like me.  The crystals are clusters, or individuals, of shiny metallic acicular crystals that are pale brass-yellow when fresh but tarnish to an iridescent “black.”  The clusters of millerite in concretions often appear, at least to me, to be a “cat’s whisker.”  However, the specimen I picked up in Tucson is completely different from the concretion specimens in that the millerite is a mass of hair-like acicular crystals---hundreds of them.  They have a measured hardness of 3.0-3.5 (Mohs), are metallic opaque, and have a greenish black streak.

Masses of millerite crystals. FOV ~2.1 cm.

The specimen I purchased has a locality listed as Biggsville Quarry, Carthage, Illinois; however, that might be the Biggsville Quarry Cessford Construction, or the nearby Cessford or Media quarries.  All are aggerate quarries of Paleozoic carbonates with minor amounts of the sulfides chalcopyrite, sphalerite, pyrite and millerite.

  

REFERENCES CITED 

Wenz, Z.J., M.S. Appold, K.L. Shelton and S. Tesfaye, 2012, Geochemistry of Mississippi Valley–type Mineralizing Fluids of the Ozark Plateau: A Regional Synthesis: American Journal of Science, v.312, no. 1, 22-80.

STAY SAFE, BE WELL

 Don't be pushed around by the fears in your mind.  Be led by the dreams in your heart.         Roy T. Bennett