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Tuesday, February 25, 2014

Barite or Baryte: A View from Cobachi, Sonora, Mexico

          Barite (spelled baryte everywhere besides the U.S) is a heavy, non-magnetic mineral with very high specific gravity of up to 4.5. It is one dense, soft rock. Barite (BaSO4) is useful in the manufacture of paper and rubber, as a tracking agent in medical tests in  the human body, and as the weighting material put into drilling fluid to keep the sides of petroleum drilling casings from collapsing and to prevent blowouts. It is readily used down boreholes as it does not interfere with any magnetic tests associated with drilling. The pinkish crystals pictured below are barite. The darker, smaller mineral is cerussite. The radiating form of barite crystals is sometimes referred to as Bologna Stone (for the town in Italy, not the lunch meat):

              The most useful variety for petroleum geologists occurs as thick sedimentary beds of pure barite with little to no silica impurities. Barite often occurs interbedded or interfingering with chert, so pure beds of thick (a meter or more) barite are highly prized:

            Pure barite needs little jigging (essentially shaking the rock in an aqueous solution), washing, heavy media separation, tabling, or flotation to be used down well bores. The barite is merely crushed to a uniform size and put in the drilling mud. 77 percent of barite is used for this purpose. And even though it is a heavy mineral, it is considered non-toxic due to its high insolubility. Deep oceanic BaSO4 deposits are useful in constraining the temperatures of oceanic crust in paleoenvironments.

            Barite in the form of desert roses is also coveted by rock hounds:

             My remarkable six-month, first adventure out of college included mapping a barite deposit in Cobachi, Sonora, Mexico. I lived with two British geologists, Rod and Kevin, and a geologist from North Carolina, Phyllis, in the little white house in the left of the photograph:

           The house had no windows, doors, or running water...but it was just $100 a month to rent. :-) Cobachi is so small (about 300-350 people) that it often does not show up on maps, even in our GPS age (though it does here):

                Mapping the barite deposit including making a grid through the desert (with the help of a local crew of ten men with machetes), scaring cows off the runway so the small plane could land, performing specific density tests, stratigraphy and paleontology including late Paleozoic fusulinids, and learning Spanish. We also hiked to the top of Sierra Cobachi with our friends from the community. They carried thick, heavy Coke bottles up and down the mountain to this stunning cave:


          This image of the people in Cobachi reminds me of how warm and kind they were to us very foreign-looking and sounding geologists. We would be treated to tomatoes on our burritos when they could afford none for their own families. They taught us to make tortillas and goat cheese and withstood us asking the same questions countless times as we learned Spanish. We took part in dances, loud wailing funerals, and evening talks about our day's adventures.

           Anaconda Barite just announced they will be upgrading the jigging plant in Cobachi early this year. So the heavy mineral barite (named from the Greek word heavy) will provide more years of economic opportunities to Cobachians. Here's hoping the heavy Coke-bottle carrying is no longer going on, though :-).

           Cobachi surely holds a heavy place in my a good way.

           Any early career adventures you'd like to share? Or your own favorite barite story?

Sedimentally yours,

Word Woman (Scientific Steph)


Tuesday, February 18, 2014

Ganymede Geology: Cup Bearer (of GanyMead?) to the gods

     Before we head to the largest moon of Jupiter, Ganymede, and leave earth's Iceland, this 1 minute and 13 second BBC clip shows the divergent (pulling apart) sea-floor spreading we discussed last Tuesday:

     The three margins described on earth in the concept of plate tectonics: (1) divergent (seen above), (2) convergent (mountain building or orogeny) and (3) transform or strike-slip often associated with earthquakes, may also play a role in the geologic formation of Ganymede.

      Ganymede, discovered by Galileo in January, 1610, has surface area that is greater than half of the surface area of the land mass on earth. The moon was named for Ganymede, the pretty boy who was taken by Zeus to be cup bearer to the gods (Had they been geologists it may well have been mead in those cups :-) ). Ganymede may be seen this month with binoculars:

      NASA released a geologic map of Ganymede this week, the first complete geologic map of Jupiter's seventh moon. The "cup bearer" stands out quite well with a blue, dark green, and purple body and green "crater head" on the right side of the first image:

     The geology of Ganymede is especially interesting to geologists because it appears there were times of tectonic movement on this icy moon. These grooves and ridges point to a similar origin to the earth's plate tectonic movement:

     In addition, periods of intense crater impacts are seen in the geologic history:

     One of the more interesting features on Ganymede are palimpsests, derived from the word meaning to write over older writing (similar to pentimento overpainting in art). [The word palimpsest is from the Greek for to scrape]:

   Similarly, older craters are "overwritten" by younger ones as the older crater margins are eroded through time:

         There were (and are) quiescent times on this frozen, icy moon (quiescently frozen :)) as well.

          There is also evidence for some cryovolcanism (eruption of  volatiles like ice and water, methane, and ammonia from volcanoes) on Ganymede.

      The link to the NASA article contains a 37 second animation so you can also see the "Dark Side of the Moon" (The Pink Floyd song turns 40 next month!):

       Looking forward to discussing Ganymede geology, nomenclature, great music, and some planetary geology jokes and puns. Do you have a favorite?

Palimpsestially,(thanks, Lego)

Word Woman (aka Scientific Steph)

Tuesday, February 11, 2014

Icelandic Plate Tectonics: No Scree-ching Halt: Give It an Inch and It'll Take A Year

     At long last, we are ready for the trip to Iceland now that the Viking Sunstone (optical Iceland spar or calcite) has been found:


     Optical calcite is rhombohedral and refracts light in a way that Norse explorers of 900-1200 A. D. were likely able to locate the sun even after sunset and on cloudy days. In those pre-GPS days, the calcite rhomb was accurate to within 1 degree:

     Optical calcite is found in abundance in the scree of Iceland, though it is now a protected resource since Icelandic tourism has recently blossomed. You may read more about calcite here, but I want to get us to Iceland, the only place on earth (currently) where a mid-oceanic ridge occurs on land:

     To repeat, Iceland is the ONLY place on our planet where one may actually witness oceanic crust being created on land. All other parts of the global mid-oceanic ridges are deep beneath the surface of the ocean. These folks are walking between two tectonic plates, the North American plate and the Eurasian plate, in Iceland:

     The theory of plate tectonics
describes the large-scale motions of the lithosphere. A good, general overview of the theory may be found here:

     The divergent boundaries between plates, known as mid-oceanic ridges, are the places where oceanic crust is created. There is a particularly good color, animated graphic in the link below (and shared here) which shows the new basalt (nicknamed MORB for Mid-Oceanic Ridge Basalt) or gabbro being created:

     Oceanic crust is richer in iron and magnesium making it heavier than continental crust, which is richer in lighter silica. The very newest "skin of the earth"  is created at mid-oceanic ridges. As one moves away from the center of the ridge, the oceanic crust is progressively older on mirroring sides of the ridge. Almost all oceanic crust is 200 million years old or younger, fairly young in geologic terms. Then, at the margins with lighter continental crust, the oceanic crust dives beneath the lighter continental crust and is essentially recycled. The major plates and their current movements are shown below:

     In Iceland, one may witness this new "baby earth skin" creation directly. In the land of fire and ice, you can actually touch this brand new earth as the mid-oceanic Atlantic ridge runs right through Iceland:

       The Eurasian and North American plates are moving apart at the rate of about an inch a year. There is no scree-ching halt to the oceanic plate movement due to the convection currents in the earth. The convection is akin to heating up pudding on the stove. The rising hot pudding comes to the surface then plunges back down again as it cools at the surface. 

        To witness new earth being created is, for me, amazing. After seeing the volcanos, ice, spar, and other Icelandic delights, here's that optional side trip to the Lucky Leif bridge in southwestern Iceland. It's a moment to ponder the earth's dynamic nature while straddling the two tectonic plates. Our trip would have been unabridged without it. :-) Enjoy!

        I welcome your comments, insights, and any sparring. 

      Here's to MORB excitement with all of you gab-BRO and SIS enthusiasts,

      Word Woman (aka Scientific Steph) 


Tuesday, February 4, 2014

Ooids, Pisoids, and Kidney Stones: Concentrate Concretely!

     The trip to Iceland with a discussion of plate tectonics and mid-oceanic rifts has been postponed due to snow. This week's blog will migrate to some more tropical sedimentary features like these ooids (from the Greek for egg-like). I never wondered why Dr. Allen Curran of Smith College chose to study them in the Bahamas:

and pisoids (from the Greek word for pea-like).

      I tried to play the word ooid in a recent Scrabble game; the Official Scrabble Dictionary says it is not a word. Oo id is! Pisoid is also not acceptable~~and it's such a fun word.  .  .

     The main difference between the two sedimentary concretions is their size. Ooids are less than 2 millimeters in size and pisoids are 2 millimeters and greater in size. Ooids and pisoids are spheroidal, layered or coated grains, usually composed of calcium carbonate (CaCO3). Some pisoids and ooids contain iron (siderite for you Latin fans) or phosphates as well. They form as a series of concentric layers (see thin section below--crossed nicols or not--you be the judge!) around a nucleus of a crystal, shell fragment, or other small grain in shallow seas where the water is highly concentrated in calcium carbonate.

     And if you use a scanning electron microscope (SEM) to view ooids you will see not only the concretions that mark the growth of ooids, but also the pitting and cracking of the grains caused by various microbes:

      Three interesting things you should know about ooids and pisoids:

      (1) They have formed under different conditions called calcite seas (where low-magnesium calcite is the primary CaCO3 precipitate and which occurred during my favorite period, the Jurassic, and the Ordovician period) or aragonite seas (where aragonite and high magnesium calcite is the primary CaCO3 precipitate during most of the rest of geologic time, including now)Thus, the calcite seas are found in the early Paleozoic time period when life was relatively new and during the middle of the Mesozoic (sometimes called the Age of Dinosaurs). Both of these time periods were time periods of rapid sea-floor spreading. (Ok, a wee bit of plate tectonics today).

       (2) Ooids and pisoids generally require microbial action in their formation.

       (3) They cannot form in areas where a great deal of river runoff occurs as the ooids and pisoids need greatly concentrated waters full of CaCO3 to form. This brings us to the kidney stone tie in:

       It had not occurred to me until today that the process of ooid and pisoid concretion is similar to kidney stone formation (It even says so in Wikiipedia :-)). Kidney stones tend to form in patients with concentrated urine (no extra fresh water running in). 

       Oh, a fourth item:

       (4) Ooids and pisoids ought to be Scrabble-acceptable words. 

       And to bring this concentrated topic concretely back in focus, this view of pisoids shows the highlighted concreted layers that have been colorized to show the structure of the layers.


        Looking forward to your crystallized, concentrated comments, diluted not at all by your new-found enthusiasm for the ooid and the pisoid :-)

        Ooidally (but not pisoidally this evening),

        Word Woman (Scientific Steph)