Thursday, May 27, 2021

REDO #2 TUCSON: COPPER, ANATASE, VESUVIANITE; GROSSULAR & TITANITE

 

In a previous posting I noted that a two-day excursion to the Tucson 2021 Redo was enjoyable and I came home with a few treasures!  Of course, I consider most of my buys as treasures although a few stinkers appear now and then.  Remember, as Bob Jones coined the term, I am a frugal collector.  I purchase less expensive specimens that “make me happy.”  I am not collecting for exhibits, or even local mineral shows, but for specimens that I can study and learn from.  Being a life-long learner is a high priority in my life!  Life is too short to be anything but happy.

Happiness, true happiness, is an inner quality. It is a state of mind. If your mind is at peace, you are happy. If your mind is at peace, but you have nothing else, you can be happy. If you have everything the world can give - pleasure, possessions, power - but lack peace of mind, you can never be happy.            Dada Vaswani   

Living in the Plains, Midwest, and West over the decades, I am not overly familiar with the geology of the Appalachian chain  of mountains. Oh, I have driven through and camped several times, I can spout off the creating orogenic events, and the physiographic provinces, etc. but outside of a few famous collecting localities/mines I remain a novice learner when it comes to the minerals.  That is one reason I enjoy the professional, but semi-hard core, journals like Mineralogical Record and Rocks and Minerals. I joined the Baltimore Mineral Society to get a non-western U.S. perspective on geology and minerals and now read several eastern mineral club newsletters if they are available on the Web.  Life is interesting.

I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived.    Henry David Thoreau

At the Show I was able to pick up a hunk (5 cm. X 8 cm) of mostly native copper with a little calcite and perhaps a few other minerals. It had been cleaned with acid so the copper would show and looked like the nuggets from Michigan that originally had been released from the Precambrian basalt by Pleistocene glaciers.  However, my purchased specimen came from the Blue Ridge portion of Pennsylvania, a state that I did not realize produced copper. The Pennsylvania Geological Survey noted that a small area (about 1- by 5-mile belt) contains trace- to minor amounts of native copper in Adams and Franklin Counties and my specimen was labeled as collected from Pine Mountain, Adams County. This is a general location of native copper deposits lying west of Blue Ridge summit.  MinDat notes the presence of native copper in epidotic rhyolite, massive quartz and associated secondary copper minerals.  No specific quarry or prospect was noted with my specimen.  Unlike the Michigan nuggets that were released and transported by glaciers, the Pennsylvania copper belt fell ~35 miles short of glacial activity so copper nuggets were never released from their enclosing metabasalt (part of the Precambrian Catoctin Formation). The Pennsylvania Geological Survey has identified eight named mines, and numerous small prospects, that are known in the native-copper belt, but production has always been minimal. Unlike many copper deposits in the western U.S. that are associated with intrusions and hydrothermal activity, R.A. Landy, in a 1961 unpublished Ph.D. thesis at Penn State, believed[M1]  that the native copper deposits were developed from the rearrangement and reconcentration of the copper originally present in the rock itself (the metamorphosed basalt).  The original basalt came from flows resulting from crustal expansion in the late Precambrian—continents or proto-continents pulling apart.


Copper nugget from Pine Mountain, Pennsylvania.  Width ~7.5 cm.

I also picked up four specimens from Lehman Minerals, collectors on the opposite side of the country—the White and Inyo Mountains of California.  Chris Lehman is headquartered in Bishop, the only city in Inyo County and situated at the head of Owens Valley between the Sierra Nevada (on the west) and the White Mountains (on the east).  The Whites are interesting from several points of view including the presence of Late Proterozoic (latest Precambrian) rocks that represent sediment shed off the early North American (in today’s geography) continent.  These rocks confused geologists for decades as they often contained fossils older than the Cambrian trilobites (and commonly were soft bodied).  Were they Cambrian in age? Or Precambrian? They were often referred to as being Eocambrian in age, but stratigraphers finally settled on Ediacaran (see Posting April 13, 2017) for that particular period of time.

Above these Precambrian rocks is a thick section of mostly shallow water marine sedimentary rocks of Cambrian (a continuation from the Ediacaran) and Ordovician age. However, the Ordovician sedimentary rocks, along with a thick section of later Mesozoic metasedimentary and metavolcanic rocks were brought into the Whites (current geography) from the northeast sliding along large scale thrust faults.  Geologists call these foreign rocks allochthonous rocks.  This turmoil continued and in the Mesozoic all sorts of crap broke loose as the Pacific Plate and others (mostly microcontinents) were banging into the North American Plate with the former being subducted beneath the latter (although some western rocks were stuck onto the North American Plate).  The subduction, with later heat and melting at depth, resulted in large scale plutonic events (magma rising towards the surface but cooling and crystallizing before reaching the surface).  Such was the case in the White Mountains but to the west the Sierra Nevada plutonic event was even more massive as these mountains are much larger that the White Mountains.  The collision of these plates rippled across western North America creating orogenic events as it proceeded.  The Cenozoic was marked by two major “happenings”: massive volcanism, especially in the mid to late Tertiary; and the crustal extension resulting in the creation of the fault block mountains of the Basin and Range.  In fact, the White Mountains are the westernmost range of this physiographic province.

The above explanation of the geology of the White Mountains is not very understandable and is critically short on details.  However, there are hundreds of professional papers scattered in libraries, and sometimes on the Web, that would be tough to synthesize in a posting like this.  The geology is complicated!

I have yet to see any problem, however complicated, which, when looked at in the right way did not become still more complicated.     Paul Anderson

Chris Lehman has a collecting locality east of Bishop that MinDat refers to as the Lehman Anatase Prospect. I am fairly certain two of my four specimens came from that location; however, the other two specimens are listed as from the “White or Inyo Mountains.”   I suppose they are proprietary locations. 

One specimen from the Lehman Prospect consists of water clear and terminated quartz crystals arranged in a spray.  The anatase occurs as inclusions within the quartz with additional anatase crystallizing on the exterior. The Quartz Page defines three types of inclusions in quartz: 1) Protogenetic where the minerals formed before the quartz and were engulfed by the growing quartz; 2) Syngenetic where the inclusions and the quartz grow simultaneously; and 3) Epigenetic where during the growth of the quartz crystal there is a pause that allows new incompatible elements into the crystal structure.  The specimen from the Lehman shows syngenetic crystals of anatase embedded in the quartz and are termed phantom crystals.


Water clear quartz crystals mounted on a pin (white).  Note anatase inclusions and external growths. Length of largest quartz crystal ~1.2 cm.

A second specimen from Lehman is a larger quartz crystal covered with quite tiny greenish brown crystals of anatase with a few crystals of adularia (potassium aluminum silicate).  The large crystal may also be included; however, the exterior growth prevents peeking into the quartz.

Quartz crystal with heavy anatase inclusions and upper crystal face covered with very tiny crystals.  Note two adularia crystals.  Length of large quartz crystal ~3.5 cm.


Adularia crystals each about 2 mm.




Green anatase crystals ~.5 mm, or less, in length.

Anatase is a titanium oxide, one of three polymorphs of TiO2—the other two being rutile and brookite.  There seems to be at least three other forms of titanium oxide that were identified in meteorites and therefore are exceedingly rare. Anatase is the least stable of the polymorphs and forms at lower temperatures and at later stages in crystallization, often associated with quartz and adularia. Belonging to the Tetragonal Crystal System, anatase usually appears as tabular or “double pyramid” crystals and are usually “green” or brown (although crystals may have a variety of colors).  It has a metallic luster is essentially opaque with a hardness of ~6 (Mohs). Titanium oxide is mostly found in metamorphic rocks and pegmatites.

The small adularia crystals [KAlSi3O8] belong to the Feldspar Group and actually are a low temperature variety of orthoclase (a potassium or K Feldspar).  Adularia crystals commonly are glassy and transparent and often tough to identify unless they have a moonstone sheen and play of colors.

A third specimen is from the nearby Inyo Mountains and is a single, prismatic, pretty ugly, crystal of epidote [(Ca2)(Al2Fe)(Si2O7)(SiO4)O(OH)]  with an attached tiny, twinned crystal of  titanite, a calcium titanium silicate (CaTi(SiO4)O), formally called sphene due to its wedge shape.  Crystals have an adamantine luster, are translucent to transparent with a white streak and a hardness of ~5.5 (Mohs).  It appears in igneous and metamorphic rocks. Not an exceptional specimen but one that is interesting with the attachment.



Titanite twin attached to epidote.  Total length of epidote ~8mm.

The 4th Lehman specimen is a group of vesuvianite crystals on a matrix of grossular (Garnet Group).  The vesuvianite [Ca10(Mg,Fe)2Al4(SiO4)5(Si2O7)2(OH,F)4] forms beautiful crystals that are either long prismatic and columnar, or short pyramids, with a greenish yellow to yellow brown color.  They have a vitreous luster, are brittle and fracture easily, and a hardness of ~6+ (Mohs). Most crystals on this specimen are fairly translucent.  Vesuvianite usually form in skarn deposits (limestone subject to contact metamorphism). See a previous Posting, November 18, 2012, for additional information.



Crystals of vesuvianite.  Width FOV ~6mm. 


Mass of grossular garnets.  Width FOV ~6mm.

Grossular is a calcium aluminum silicate [Ca3Al2(SiO4)3] that often is some sort of a green color since it is named for the color of gooseberries. It is a common mineral in contact metamorphic zones associated with limestone, and is an associate of vesuvianite, wollastonite and diopside. 

The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom.   Isaac Asimov

 

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