SI AND URA
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A WILD RIDE FOR TWO LITTLE BUDDIES

by

Tommy R. and J. Frank Woodward II

          Once upon an eon when they were just tiny floating atoms they developed a close friendship of common interests. It was surprising they even knew each other considering they came from such different places in life: Si, with an atomic weight in the neighborhood of only 28, was rather small and slightly puny for his size, whereas Ura was from all the way across town and had an atomic weight of 238. This made Ura much heavier and muscular than Si, but that worked to his advantage because he was always protecting Si from the neighborhood molecules who kept trying to consume him. Of course it didnít hurt that Ura was radioactive which kept many molecules away from them both. Seems radioactivity didnít bother Si very much.

         Later, when Si and Ura began developing into molecules, the next stage of most all molecular structures, they became even more closely bonded. Si joined up with some Oxygen molecules (O2) to become SiO2 (silicon dioxide). There were other Silica Groups (SiO2) running around like quartz (including names such as agates, amethysts and chert) tridymite, cristobalite, and opal. Ura also found some oxygen molecules and became U3O8. Some of Uraniumís relatives, such as pitchblende and thorium, were there too. They were all running around and playing together: sometimes as a group. Seems they all had a common bonding.

         Now, as you might know, this huge volcano was like so many other volcanoes around the world. Occasionally they rumbled. And when they rumble they act like any other volcano in that their stomachs get so upset that they begin to throw up just like anyone would with an upset stomach. When this happens to volcanoes their insides of molten rock from deep down in the earth will begin erupting to the surface. Upon reaching the surface so much pressure would be released that lots of lava was thrown way up into the air. Sometimes many miles high.

         We begin to wonder what has happened to Si and Ura and all their tiny friends! Well, as you might have imagined, they got all caught up in this tumbling and erupting and found themselves thrown very high into the atmosphere above the earth. They are all so scared that many developed a natural tendency to cling together tighter than they ever have before. Many large chunks of lava of all sizes cooled enough and turned into rocks of all sizes. Of course, now as they cling together they gather enough weight and begin falling back to earth.

         As Si and his friend Ura and many others kept desperately clinging together, hoping to not get hit by all this falling debris of rocks all around them, they began to realize that the upper air and wind currents were carrying them away from the volcano and away from all this dangerous debris. This scares them even more as they realize they will never see their home and many of their friends ever again.

         [Dear reader, let us digress a few moments to explain to you the situation at hand. This liquid rock where Si and Ura lived, this magma chamber of molten lava below this huge volcano could well have been, and was, the same volcano that existed in the far western part of the Big Bend of Texas during geologic times. The core of this old volcano is now called Chinati Peak and exists in the Chinati Mountains of Presidio County Texas, was created during the Laramide era of past geologic time. But at one time it burst on the scene as yet another huge volcano in the chain of volcanoes many hundreds of miles both southeast and northwest. Little did Si and Ura realize they were being carried eastward by the winds to what will later be called southeast Texas, southern Louisiana, Mississippi, Georgia, and northern Florida.]

         Si and Ura were now falling from the sky. The winds had died and they were just drifting along, but slowly getting closer to the ground. They could see that they were being carried lower and lower toward a large forest of trees (mostly palm wood) that had recently been buried by the same ash fall. Now they were drifting down toward the trees and they really hung on tight to each other. Upon gently landing they found the environment to also be very wet. They had never seen a water environment before so they were really frightened as to what may happen to them next.

         They didnít know that some waters have a very alkaline environment and that it also includes other atoms such as lithium, sodium, potassium, rubidium, cesium, and francium.

         As it so happened, they discovered they had landed on a tree which had been buried by the ash fall. What a surprise! Many of their old friends and buddies were already on the old log. But also were many from the other clans. They were especially scared of the cesium and potassium clans.

         After much reunion and talk about what had happened, and what were they going to do next, they began to worry about their fate. Some said they should abandon this old log and try to find a better home. Some said they should all separate and strike out on their own in order to find a way to survive. Some said maybe they should try making friends with some of the other clans. After all, some were closely related, but simply had never met. Ura was especially attracted to several because they were also radioactive, but not as much. But in the end, they all decided to stick together and make a new home in what was left of this old dead tree.

         Meanwhile, the environment was becoming more and more alkaline (non-acidic) from the tuffaceous volcanic ash material. They appointed scouting parties to look around and see what their new home was going to look like on the inside. It was soon discovered that the tree wasnít floating but was actually stuck deep in some of the ash material from the same volcano they had all drifted away from through the air. Deep within the old water-logged tree they found empty spaces of porosity with good permeability that allowed them to enter an environment that looked to be of their suiting. The porosity furnished the openings in which Si and Ura, and their many friends within their clan, could squeeze into the porous but rolling cells. Just like exploring caves. The permeability furnished the ease in which they were able to squeeze through the pores of porosity from one cavity to the other. They finally arrived somewhere near the center of the old log, which was more acidic due to the decaying log, where they found what they wanted and decided to stay awhile.

         But as it turned out the moisture and tuffaceous material, being an alkaline environment of alkali carbonates, was forcing many Silicas and Uraniums to not begin bonding and run away downdip while some moved into the cells and other acidic rotting cavities of the wood. Soon they got so big that were not able to get out of their rapidly filling space within the log. They were stuck in gel. The rotting log was creating a more acidic environment and accelerating the situation. Si and Ura, along with many O2Ďs started growing and bonding by latching onto each other.

         They were now being surrounded by more and more silica gel, and possibly opal, which both are more soluble in water than quartz. The pores had now shrunk too small and no amount of permeability would allow them to leave. The more they bounced around the larger they became until finally they realized there would never be any escape from their vuggy old wood cell, so it was decided they would just stay and enjoy being close to their new many friends for a long, long time.

         As time passed, Si gradually merged with other silicons to eventually become chalcedony, or agate, while Ura became quite attached to carnotite. But Si and Ura were still close enough to be friends Ė forever.

carnotite in petrified wood

Fig.1 Silicic petrified wood with carnotite (yellow) imbedded. Under a microscope
or hand lens can be found black pockets of Uraninite or Pitchblende.

         Here they are today: uranium enclosed by silica (chalcedony) within a slab of petrified wood containing carnotite (yellow), and located within the Upper Tertiary (Oligocene?) Catahoula tuff formation from Karnes County, Texas. Si and Ura had happily resided there together for over 35 million years.

         We now also know that the volcano near Shafter, Texas violently exploded in a past geologic time sending those identifiable silicon and uranium molecules drifting with the winds to be deposited in southeast Texas and Louisiana. The extruded lava in west Texas was named the Buckshot Ignimbrite.


REFERENCES

Amsbury, D. L., 1958 Geology of the Pinto Canyon area, Presidio County, Texas: Univ. Texas, BEG, Quad Map No. 22, with text.

Dietrich, J. W., 1966 Geology of Presidio area, Presidio County, Texas: Univ. Texas, BEG, Quad Map No. 28, with text.

Eargle, D. Hoyle, 1969 United States Geological Survey, Austin. Texas Office of Radioactive Minerals (personal communication to J.F.W.).

Maxwell Ross A., and Dietrich, John W., December 1970 Correlation of Tertiary rock units, West Texas: Univ. Texas, BEG, Report of Investigation No. 70.

__________________________________, 1965 Geologic Summary of the Big Bend region: West Texas Geol. Soc., Field Trip Guidebook, Pub. 6711.

Simpson, Brian, 1966 Rocks and Minerals: Pergamon Press, London, reprinted 1969.

Woodward, J. F., Jr., 1969 A Summary of the Tertiary geology in Trans-Pecos and its relation to the rocks and mineral deposits in the Gulf Plain: © 1969; privately published by Meeker & Company, Ft. Worth, Texas.


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