Monday, October 23, 2017

SMITHSONITE: TURKEY FAT




Nary a leaf has left the tree.  Quiet and calm.
How silently they tumble down
And come to rest upon the ground
To lay a carpet, rich and rare,
Beneath the trees without a care,
Content to sleep, their work well done,
Colors gleaming in the sun.


At other times, they wildly fly
Until they nearly reach the sky.
Twisting, turning through the air
Till all the trees stand stark and bare.
Exhausted, drop to earth below
To wait, like children, for the snow.

-   Elsie N. Brady, Leaves
 
A day later the wind came up, it snowed on the pass, and leaves dropped.
Thanksgiving is soon approaching, and the magic day will appear next month on the 4th Thursday.  This holiday is one of my favorites, if celebrated as first intended—a harvest festival, and not as a commercial gift buying frenzy.  I enjoy the days around Thanksgiving because of the “smells” -- it is almost olfactory overload.  Virtually every smell this time of year reminds me of my childhood—burning leaves, baking pies (I love mincemeat), scalloped oysters, baked winter squash with brown sugar, roasted apples (with cinnamon candies in the hollowed core), scalloped rutabaga and many other things (but not pumpkin pie).  If that is not enough there is always the sight and hearing---especially trilling cranes and honking geese several hundred feet in the air heading south.  And if I am really lucky, a weekend snow storm.  But, the smells are what makes the connection to my youth.

The wild gander leads his flock through the cool night,
Ya-honk!  he says, and sounds it down to me like an invitation:
The pert may suppose it meaningless, but I listen closer,
I find its purpose and place up there toward the November sky.

-   Walt Whitman, Leaves of Grass, 1855

I sort of remember my 8th grade health and later college biology courses; however, the actual schematics for hearing have sort of escaped me.  So, if you really want to know how smell works (courtesy of Gloria Rodriguez-Gil, M.Ed., California Deaf-Blind Services Educational Specialist; Reprinted from reSources, Spring 2004, Volume 11, Number 2): 
The process of smelling goes more or less like this:
1.    Vaporized odor molecules (chemicals) floating in the air reach the nostrils and dissolve in the mucus (which is on the roof of each nostril).
2.    Underneath the mucus, in the olfactory epithelium, specialized receptor cells called olfactory receptor neurons detect the odor. These neurons are capable of detecting thousands of different odors.
3.    The olfactory receptor neurons transmit the information to the olfactory bulbs, which are located at the back of the nose.
4.    The olfactory bulbs have sensory receptors that are actually part of the brain which send messages directly to:
o    The most primitive brain centers where they influence emotions and memories (limbic system structures), and
o    “Higher” centers where they modify conscious thought (neo-cortex).
5.    These brain centers perceive odors and access memories to remind us about people, places, or events associated with these olfactory sensations.

So, back to Thanksgiving.  I am not a big fan of baked turkey, or any other renditions of “left-over” bird.  However, baked turkey reminds me of a trip to Arkansas many years ago and learning about turkey fat.  Yep, as as in turkey fat ore!

Turkey fat ore is an old, but common, name for a variety of the zinc carbonate, smithsonite (ZnCO3).  Originally the name applied to botryoidal and globular smithsonite colored various shades of yellow by traces of cadmium (Cd). The “globs” reminded early miners of turkey fat (the real stuff).  Later in life, a couple (maybe others) of mines (Philadelphia and Monte Cristo) in the Rush Creek Mining District in Marion County, Arkansas, started producing yellow smithsonite replacing and/or coating well-formed, curved and saddle-shaped dolomite crystals and the name turkey fat ore was applied--no globs here.. Many Arkansas specimens also display sphalerite (ZnS), the primary sulfide precursor, and secondary quartz and calcite.

Yellow, cadmium-rich smithsonite crystals have pseudomorphed, or replaced, earlier formed curved, saddle-shaped dolomite crystals.  There are also very tiny crystals of quartz (Q: evidently secondary).  Width of photo ~1.6 cm.  The perimeter of the photo is a styrofoam background.  

The Rush Creek Mining District is in northern Arkansas in the Ozark Plateaus Physiographic Province.  The Arkansas Geological Survey (2017) noted that the northern Arkansas area has been of commercial importance for production of lead (galena) and zinc (sphalerite, smithsonite and hemimorphite—zinc silicate).  The zinc and lead minerals are present in Paleozoic carbonates and chert beds.  Zinc has always been secondary to lead mining but does have a long history in northern Arkansas—1857 to ~1962 with peak production during World War I.

Saddle-shaped and curved dolomite crystals that are accentuated by iron staining.  Specimen width ~5.5 cm. The white globs are calcite.  Specimen collected from Mattie May Mine in the Rush Creek Mining District.

Photomicrograph of above specimen.  Note curved crystals.

The mineral sphalerite, a zinc sulfide usually containing various amounts of iron, is the primary source mineral (hypogene) for about all oxidized (secondary or supergene) zinc minerals such as smithsonite and hemimorphite.  The exception to this statement is the zinc ore at the very geologically unique deposits at Sterling Hill and Franklin, New Jersey.  That place is a story for another day.

Primary sphalerite, width ~1.2 cm., collected from Mattie May Mine.

The original sphalerite formed in the absence of oxygen in a reducing environment. When percolating and oxygenated water, often helped along by oxidized pyrite producing sulfuric acid, reached the sphalerite it became unstable and broke down (oxidized). When these acidic waters, rich in zinc, reached the host rock dolomite, the carbonate smithsonite was deposited.  At times, the original dolomite was completely dissolved.  In a few instances, such as at Rush Creek, the original dolomite crystals were replaced by smithsonite (pseudomorphs) while retaining the original shape.

Cadmium is a common trace element in sphalerite and therefore is available to add the yellow color to smithsonite at Rush Creek---I think!  However, some noted mineralogists believe the color of turkey fat ore is caused by a mixture of cadmium and greenockite (CdS).  In fact, Robert Lavinsky, in describing a specimen on MinDat stated:  The colour of your specimen is caused by greenockite inclusions, i.e. it is a mixture of smithsonite and greenockite, but NOT a cadmium smithsonite. Unfortunately, the term "cadmium smithsonite" is widely applied to these materials in the mineral market. Nevertheless, this is totally wrong. OK, the coloring is due to some sort of cadmium!

At any rate, the pseudomorphs from Rush Creek are recognized by rockhounds everywhere. 

Another little tidbit of trivia.  The November full moon will occur on November 4, 2017, and is known as the Beaver Moon.  At Thanksgiving on the 23rd the moon will be waxing but less than the First Quarter (November 26).  The Hunter’s Moon appeared on October 5, 2017 and was absolutely spectacular here in Colorado.  This year the Hunter’s Moon was also the Harvest Moon, the full moon that appears closest to the Autumnal Equinox (September 22, 2017).  Now you know,



REFERENCES CITED




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