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Nice fall errata and some neat mineral info from a member...

JUST IN TIME FOR THANKSGIVING:

Mike Nelson



Nary a leaf has left the tree. Quiet and calm.

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 this 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 rutabagas 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 snowstorm. 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



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 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, rhombohedral and curved saddle-shaped dolomite crystals and the name turkey fat ore was applied. Many Arkansas specimens also display sphalerite (ZnS), the primary sulfide precursor, and secondary quartz and calcite.



Yellow, sparkly, cadmium-rich smithsonite crystals have pseudomorphed, or covered, earlier formed rhombohedral and 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. Collected Rush Creek Mining District, Arkansas.



Rhombohedral crystals of dolomite partially pseudomorphed by yellow smithsonite. There are also botryoids (globs) of smithsonite mixed with the dolomite. A stray quartz crystal or two are evident. At first, I thought quartz was epitaxial on dolomite and then covered with smithsonite. I now believe the sparkles are created by scalenohedral smithsonite. Width specimen ~1.0 cm.

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.



These are non-pseudomorphed, 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.



Primary sphalerite, width ~1.2 cm., collected from Mattie May Mine, Rush Creek Mining District.

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.

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 and the smithsonite pseudomorphs from Rush Creek are recognized by rockhounds everywhere!

Another little tidbit of trivia. The November full moon will occur on November 30 and is known as the Beaver Moon since the critters had developed their full winter coats and Native Americans, along with European immigrants, thought it was a perfect time for trapping. At Thanksgiving on the 26th the moon will be waxing gibbous, about 87% visible (plenty bright for an evening stroll to work off the pie). The Hunter’s Moon appeared on October 31st and was a spectacular Blue Full Moon here in Colorado. It is hard to believe but full moons on Halloween are rare. The last one to appear in all U.S. Time Zones was in 1944. If you missed the event the next is scheduled for 2039. All Halloween full moon are Blue Moons, the second to appear in one month. Moon Cycles are 29.5 days long while the Gregorian Calendar has cycles ranging from 28 days to 31. Now you know. I want to wish all my friends in South Dakota Happy Thanksgiving.

REFERENCES CITED

Arkansas Geological Survey, 2017: http://www.geology.ar.gov/minerals/metallic_descriptions.htm

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