AENIGMATITE--THE RIDDLE IS SOLVED

ENIGMA

1. puzzling or inexplicable occurrence or situation

2. person of puzzling or contradictory character

3. a saying, question, picture, etc., containing a hidden meaning

(courtesy dictionary.com)  

As a kid I was not really interested in puzzles or riddles but was a voracious reader.  Unfortunately, I still am not interested in puzzles although friends inform me that they are good for brain health!  Is that true? Don’t know! What I do know is that my reading habits have served me well since childhood and are still a joy today.  My current play list includes a series of books written by the British naturalist Gerald Durrell, rereading River Horse (William Least Heat Moon), and a new bio on Jim Bridger.  In addition, throw in the journals like Rock and Gem and Rock and Minerals as well as a slew of club newsletters.  In a final bit of trivia, Least Heat Moon and I were co-presenters at an undergraduate research symposium and shared a cold IPA together one evening.

My early reading also got me interested in cryptography, and in an enigma, no not a riddle nor the band but a cipher machine used extensively by Nazi Germany during World War II.  These devices used algorithms to code, and ultimately send via wireless, messages to the military units who in turn had an identical machine to read the code and then use a key to decipher.   Very simple encryption might use the key “shift 6.”  So, MJXE could be sent and translated to ROCK as can be seen from shifting letters in the second line.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

V W X Y Z A B C D E F G H I J K L M N O P Q R S T U

Now, the Nazi Enigma Machine was much more complicated than this simple example (termed a Caesar Cipher) and was used extensively to send secure encryptions, top-secret information---or so the Nazis thought.  It turns out that a group of Polish cryptologists, working with British colleagues out of the famed Bletchley Park, “cracked the Enigma cipher” and substantially shortened the war effort (perhaps 2-4 years) and perhaps even “won the war” for the Allies. The code breaking at Bletchley Park remained classified information until the 1970s.

An Enigma Machine at the Imperial War Museum, London.  Photo Public Domain courtesy of Karsten Sperling.

 

Back to my kiddiehood---simple encryptions (Caesar Ciphers) were an important part of our boyhood games.  Each play day the “code” would change from “shift 6 to shift 3” etc. Some days the code would be written with lemon juice and the paper needed heat to allow the juice to turn a brown color so it could be read.  At other times our teachers would use encryptions as a learning tool—the code shift today is (6+3)x2(÷3).  In looking back, I learned much with out the use of computers and other electronic gizmos just as Ralphie did in the movie The Christmas Story—Be sure to drink your Ovaltine coded out on his secret decoder ring. Actually it was a decoder pin and if this mundane bit of trivia confuses you, see the movie.  

 ck to m

But back to the mineral of the day. Aenigmatite was named in 1865 and mineralogists were uncertain of its chemical composition, an enigmatic situation, a riddle.  This ranks very high on my list of the best derived mineral monikers.

Igneous pluton

A rare aenigmatite forms

Rich in sodium

Think I did it---5 syllables first line, 7 the second, 5 in the 3rd. That makes a haiku. Right?

 

Aenigmatite, length of crystal 3 cm. Collected from Mt. Eveslogchorr, Khibiny Massif, Kola Peninsula, Russia.

I purchased this specimen of aenigmatite shown above since: 1) it was a  beautiful prismatic crystal; 2) it was one of those strange, igneous, silica-poor, aluminum-poor, sodium-rich minerals that often occurs with aegirine-augite, astrophyllite, arfvedsonite, riebeckite, hedenbergite, fayalite, and ilmenite in alkaline volcanics and pegmatites.  Good exposures of these rocks occur in exotic localities with unpronounceable names such as the Ilimaussaq intrusion in Narssarssuk, Greenland, and the Khibiny and Lovozero massifs, Kola Peninsula, Russia.  These are places where the average rockhound will lack access for collecting! However, there might be collecting locality closer to home???  MinDat noted (7 December 2021) that aenigmatite was known from the Mt. Rosa Granite (a sodic igneous pluton), part of the greater Pikes Peak Batholith (~1.08 Ga) near Colorado Springs.  Unfortunately, MinDat did not provide photos.  Since Eckle, in his tome on minerals of Colorado (1997), did not recognize aenigmatite from Colorado, I presume the MinDat information came from a thesis by Livingston (2020) who stated, Diverse lithologies are associated with emplacement of the complex; these included peraluminous to peralkaline granitic rocks with several associated minor rock types, such as various dikes and pegmatites. Recent geologic and geochemical studies of the complex revealed the Mount Rosa Granite to have a complex petrogenesis within the pluton. This granite is host to complex Ti-bearing minerals, astrophyllite [K3Fe2+7Ti2Si8O26(OH)5] and aenigmatite [Na2Fe2+5TiSi6O20], which are noted to represent highly peralkaline rocks….At any rate, aenigmatite is a fairly rare mineral found only in these complex alkaline rocks.

Aenigmatite, Na₄(Fe₁₀Ti₂)O₄(Si₁₂O₃₆), is a sodium, iron, titanium silicate with a black to dark brown color and an adamantine to greasy luster.  On first glance, it appears opaque but with a strong back light some crystals are translucent.  The streak is reddish brown while the hardness is ~5.0 to 6.0, call it 5.5. It is quite brittle with an uneven fracture.

The photos on MinDat seems to indicate that most crystals are pretty ugly prisms, often short and stubby, and rough or pitted in appearance.  I was concerned that perhaps my specimen was misidentified until: 1) a MinDat photo of nice shiny, striated and terminated crystal collected from the Azores (Portugal) looks very similar to mine; and 2) Rock Currier, in a MinDat best of article stated “sometimes black, well developed prisms to 10 cm are found (sometimes striated) frozen in the alkaline rocks of the Khibiny Massif… Boots Cureton says he has had specimens from there that were confirmed by microprobe that were sharp bladed, black, prismatic and striated to 4 cm.”  Two labels on my specimen indicate it was collected from Chibiny, Kola Peninsula.  So, I will go with those identifications, and a second enigma was solved! However, I have not come to terms with a third enigma--why line spacings are different within this post ?

As I attempt to finish this post on December 18, I periodically step outside to view the last full moon of 2021.  It is a beautiful sight since the skies are clear and I am able to use trees to mostly obscure city lights.  This final full moon is often termed the “cold moon” for obvious reasons, except this year in Colorado where temps are constantly above normal, and snow has not been recorded this fall/winter.  But my favorite name is “the long night moon” due to the upcoming arrival on December 21^st of the Winter Solstice, the longest night of the year (in the Northern Hemisphere) where in Colorado Springs the sun sits at 4:40 pm and rises on the 22md at 7:14 am.  Since I live on the north side of a “hill” the sun disappears mid-afternoon.  Never-the-less, a full moon and the Winter Solstice---my moments of tranquility and enjoyment.  I looked for Comet Leonard near Venus after sundown but could not really pick it out. Oh well, the full moon was OK for me.   

REFERENCES CITED

Eckels, E. B.,1997, Minerals of Colorado: Fulcrum Publishing, Denver.

Livingston, K., 2020, The Peralkaline Mount Rosa Granite: Contrasting Mineralogy and Geochemistry Observed in the Mount Rosa Granite, Pikes Peak Batholith, Colorado: Masters thesis, Colorado School of Mines). https://mountainscholar.org/handle/11124/176299?show=full 

 

 

MICROLITE: NOW I AM REALLY CONFUSED

PETROGENESIS

Crystalline magma

Solid solution forming

Behold, microlite! 

Surprise, surprise.  It is sometimes quite interesting to find a nifty mineral stuck on a shelf in the local rock/mineral store that has been displayed for a “long time.”  This fall I was visiting such a store and asked about a specimen marked $2.  The genial proprietor told me that the specimen had been part of a purchased estate and to please take it off his hands since it had not sold for months.  First, in this tourist locality no one really knew what it was, and secondly most could not even spot the advertised mineral on the specimen.  So, I shelled out two one-dollar bills for my very own specimen of microlite (well really Microlite Group) but more on that later.  I really didn’t know zip about microlite except that it contained tantalum, and at times, a Rare Earth Element or two.

In getting the specimen home and trying to locate additional information I did find out that microlite is not a valid mineral name but is a generic moniker for the 13 members of the Microlite Group (as listed by MinDat). In turn, the Group is part of a larger classification of minerals named the Pyrochlore Supergroup.  Members of both the Group and the Supergroup are difficult to distinguish between and correctly identify without the help of magic laboratory gizmos. 

The label with my purchased specimen.  

Microlite, a tantalum (along with some other cations) oxide, may contain trace amounts of niobium (a rare earth mineral, and perhaps even scandium and yttrium) since it is in solid solution with the niobium oxide pyrochlore.  MinDat notes a very complex chemical formula with many substitutions for microlite and pyrochlore; however, the $2 Amelia Courthouse specimen in my collection seems to be fluorcalciomicrolite [(Ca,Na)₂₍TaNb)₂O₆F] although the literature seems replete with authors simply calling the mineral  microlite (especially in older literature).

A single crystal of "microlite" embedded in albite var. cleavelandite.  Width of crystal ~3.5 mm.

Pyrochlore also is no longer recognized as valid mineral name since specimens may now be identified (usually not visually) as belonging to one of the 21 members of the Pyrochlore Group, part of the Pyrochlore Supergroup.  In generic terminology pyrochlore usually means the tantalum has been replaced by niobium but scientifically  such minerals are fluorcalciopyrochlore  [(Ca,Na)₂₍Nb)₂O₆F] and as stated, there is a solid solution relationship between the these two minerals. The most common occurrence of generic microlite and/or generic pyrochlore is as scattered grains in lithium-rich granites.

Microlite received its original name from the size of most crystals---small, tiny.  When one does spot a crystal of microlite, it usually has a resinous luster, a dark yellow to yellow brown to reddish brown to greenish brown color, and a yellow streak. It is subtranslucent and crystals have an octahedral outline with a hardness of ~5.5.  Crystals may be slightly radioactive.  Mostly "microlite" forms rather nondescript, small, yellow brown, resinous, slightly translucent crystals. As Simon & Schuster’s Guide To Rocks And Minerals point out, microlite is “of interest to mineralogists and collectors.”

As previously stated,  I know very little about microlite (and now I am really confused); however, I know less about the Amelia Courthouse mines except they are situated in the Piedmont Physiographic Province of the Appalachian Mountains, are/were a “famous” collecting locality for pegmatite minerals, especially industrial mica, and amazonite. Yes, the same greenish-blue variety of microcline that is a collector’s favorite in the Pikes Peak region. The mines were also noted for producing a large number of rather uncommon minerals. Grier (1994) reported that the  “Rutherford Mines Nos. 1, 2, and 3 were a series of world- famous excavations into pegmatite bodies in the vicinity of Amelia Courthouse, Amelia Co., VA. The earliest recorded mining was for muscovite in the No. I mine in 1873, but operation in prehistoric times has been indicated…From 1912 to 1932, 15 tons of gem amazonite were taken from the No. 2 mine by the American Gem and Pearl Company of New York. Commercial operations ceased in late 1959…

Outstanding specimens of microlite occur at the Rutherford Mines, finds having been recorded as early as 1881. Masses weighing at least 8 lbs. were observed in No. 1 mine, and well-formed octahedra up to 7 cm across were found in No. 2 mine… Microlite is ordinarily found in extremely small crystals, some of microscopic size, hence, the name… The composition of Rutherford microlite approaches that of the Nb end-member of the series, pyrochlore. All of the microlite specimens are radioactive due to trace amounts of uranium. The crystals vary from opaque to nearly transparent. They are brown, greenish-brown, brownish-yellow or reddish-brown in color. The crystals occur both in the interstices of cleavelandite and in the blocky albite.”

MinDat listed 54 valid minerals collected from the mines including Rare Earth Minerals, several containing tantalum and/or columbite, and others that are rare or uncommon (including some gemstones).  John Sinkankas (1968) stated the mines were “classic mineral occurrences.”  So, although my specimen is not much to look at, it adds something to my collection coming from a classic locality! 

Don't be afraid to be confused. Try to remain permanently confused.   George Saunders

The unknown, also confusing! A vug of some sort in the feldspar matrix showing gemmy, clear, elongated, and perhaps striated, crystals of an unknown mineral.  One of life's unanswered questions.  Width of vug ~3 mm. 

 

References Cited

Grier, D., Jr., !994, The Rutherford Mines: https://tgms.weebly.com/uploads/3/3/6/9/3369036/the_rutherford_mines.pdf

Sinkankas, J., 1968, Geology and mineralogy of the Rutherford pegmatites, Amelia, Virginia: American Mineralogist, vol. 53.