Tuesday, July 7, 2020

LITTLE SPHERES OF MINERALS


Remember in the mid-1980s when Buckyballs (buckministerfullerenes) came along?  They were one of the first nanoparticles to be discovered and are linked carbon atoms with the finished product resembling are spherical soccer ball.  Science was buzzing with excitement. These molecules were named after R. Buckminster Fuller, a noted architect and inventor who was credited with (at least in the U.S.) designing and popularizing the geodesic dome.  The U.S. military was the first industrial user of the dome but the free spirits (some would call them hippies) jumped on the bandwagon in the 1960s and dome tents and commune building were popular. 
The Climatron.  Photo courtesy of its home, the Missouri Botanical Gardens.
In 1933 Fuller designed, with three prototypes built, a dome-type care, the Dymaxion that perhaps in the future could fly, land and drive—WOW.  One might think that all construction in the country would soon feature domes.  But somehow the “idea” slowed and today one might see geodesic domes in the forms of tents, DOT sheds in areas of heavy snow, radar domes, biospheres, and some construction companies/shops.  However, no cars and not many houses.
One of the prototype Dymaxion vehicles. Public Domain photo.
However, the carbon molecule buckeyballs were far more successful that the geodesic domes and opened up the entire new area of nanotechnology—solar cells, 5G communication, and a whole bunch of things I really don’t fully understand!
A sketch of the carbon buckministerfullerene.  Courtesy of understandingnano.com
As the 21th Century rolled around innovative toy makers discovered that the term Buckyball was not copyright so here came the kiddie toys of round magnets (super-strong, rare earth neodymium magnetic spheres). The youngsters could now build their own models of buckyballs, or a variety of other designs including the ubiquitous refrig magnet to hold up crayon drawings. So, nanotechnologists to kiddies were having fun with buckyballs.
Buckyball constructed with magnetic "balls."  Photo courtesy dotpedia.com.
But rockhounds, being a playful bunch, could not let the designers, soccer players, kiddos, architects, chemists, physicists, engineers, etc. have all the fun with rounds balls made of whatever.  We have the geode hunters and sphere makers and even some cab designers having fun playing with minerals.  However, the most fascinating minerals shaped like buckeyballs (spheres of some sort) are usually only seen by rockhounds looking through a loupe or better yet, a scope!  There is a fascinating world that is open to micromounters, a view that is often missed by rockhounds.  Now, I am not really a micromounter (they are really skilled) but do enjoy taking a peek at tiny mineral specimens through my binocular scope and snapping a photomicrograph or two through a not-too-expensive digital camera (wishing I had focus stacking knowledge).

Di I have fun looking at little round balls?  You betcha!  The other day (celebrating firecracker day sequestered in my mineral den) I was looking at a specimen labeled beuranite, an iron phosphate, collected from the Coon Creek Mine in Polk County, Arkansas.  Something seemed wrong for beuranite identification so I looked on MinDat and the mineral was no longer listed—for any locality in Arkansas.  What I did notice was that the mineral in question was cacoxenite, an iron aluminum phosphate [FeAlO6(PO4)17(OH)12-75H2O]. Cacoxenite is often a quite attractive mineral in various shades of yellow to orange to golden to green. And, the tiny acicular crystals (crudely hexagonal, subviterous) are often found in concentric spherical aggregates.  In other words, lots of little cute balls.  Cacoxenite is a secondary mineral (like many other phosphates) in the oxidation zone of ores of iron.  At Coon Creek Mine the mineralization is in fractures of novaculite (fine grained siliceous rock).


Acicular crystals of cacoxenite found in spherical aggregates.  Each "ball" is less than 1 mm in diameter.  The matrix is probably some iron phosphate.
  Cacoxenite is just one of many phosphate minerals that occur in a variety of spheres, minerals like kidwellite, rockbridgeite and wavealite are common examples.

At the same time I was looking at the Arkansas specimens I picked up a stray on my desk labeled leucophosphite from the Czech Republic.  As a curious sort of person, I stuck the specimen under the scope expecting to see a reddish-orange mineral (I did, the leucophosphite) but also observes a passel of “little balls.” At first glance one might think insect eggs-nope, a bunch of spherical minerals. Somewhere in the back recesses of my mind I recognized the mineral so off I go to MinDat to confirm it was meurigite.  Actually the people in the know have added a k on the end (meurigite-K)  to distinguish the potassium dominant form from the sodium dominant meurigite-Na.   The mineral is another of those potassium iron phosphates [KFe8(PO4)6(OH)7-6.5H2O] that only Tom up at Dakota Matrix can distinguish apart.


Submillimeter spheres of acicular crystals of meurigite-K on a matrix of black goethite? (bottom) and red to red-brown leucophosphite (upper two photomicrographs).  Leucophosphite is another hydrous potassium iron phosphate.
Meurigite-K is yellow to yellow-green to yellow-brown to white in color composed of radial acicular sprays that usually show a concentric pattern on the inside of the spheres. My specimen came from Těškov, Rokycany District, Plzeň Region, Czech Republic.  

As noted above many phosphate minerals have this spherical appearance with acicular crystals radiating out from a center.  As with many phosphate minerals, I failed to fully (or even partially) understand their mineralogy or provenance.  Most of these “little balls” are secondary occurrences in the oxidized zone so I assume that primary phosphate minerals were the original source.  As for the “cause” of these “little balls” of radiating crystals, it is one of life’s persistent questions that is above my skill level of understanding.

The fact that you are willing to say, “I do not understand, and it is fine,” is the greatest understanding you could exhibit. Wayne Dyer