Uraninite

Specimen #1

Specimen Notes Occurrence - The host rock is quartz sandstone heavily impregnated with Uraninite. The Uraninite also occurs as a 1.5 cm thick vein in a crack in the sandstone. Through the approximate center of this vein of Uraninite is a 2 mm thick vein of yellow Zippeite nodules. Crystals - There are no crystals of Uraninite found anywhere on this specimen. The Uraninite is in fine grains in the sandstone, and as a solid mass within the vein. The Uraninite in the vein has a glassy appearence that has a discernable choncoidal fracture. This indicates that it is not formed by reduction by decaying organic matter, but by deposition from a percolating solution. Appearence - The Uraninite has a luster that varies from vitreous in geologically fresh surfaces, to earthy in areas that are weathered. It's diaphaneity is opaque, with a black color. The color can be brownish-black in weathered areas, and within the sandstone.

Specimen #2
Petrified Wood

Specimen Notes Uraninite Petrified Wood - This specimen of Uraninite is an excellant example of uranium dioxide (uraninite) being deposited on, and replacing, organic matter. Hexavalent uranium (U+6) is more soluble than quadavalent uranium (U+4). As burried organic mater decays, it creates a reducing environment around itself, which causes the U+6 in solution to be reduced to much less soluble U+4, which precipitates out as Uraninite. Image 001a shows a corner of the specimen that has nearly all of the cells of the replaced wood open, while the uraninite has replaced the cellulose. This is best seen in the high resolution image (click on '001a'). The specimen has been cleaved in the plane of the petrified wood layers, exposing the cell structure. To the right of this area, the specimen was cleaved at an angle to the petrified wood layers, and this pattern of striations is all but hidden. The type of patterning, and lack of gloss, seen in this area is the most likely what will be seen on other uraninite petrified wood specimens. In image 001b, the petrified wood cell structure is filling in, making the cell structure less obvious. The cleavage plane is at an angle to the petrified wood layers, and reveals this layering as it alternately cuts through these layers (similar to the year rings in wood) and parallels them. Image 001c shows an area where the cells of the petrified wood has been almost completely filled in. Only a very few cells remain open, and appear as dark oblong shapes that are all parallel to each other. The only indication that this is uraninite petrified wood is the grain of the specimen that parallels these few open cells. In specimens that are highly mineralized, it may be only with very high magnification, or examining a polished section, that the petrified wood nature of the uraninite specimen will be revealed.

Specimen #3

Specimen Notes Occurrence - The specimen is on Calcite host rock. This calcite appears to be very crystaline, with some indication of having undergone early stages of metamorphosis to Marble in some areas. The Calcite shows a visable layering that, under a microscope, is still visable, but is less obvious due to the random orientation and partial metamorphosis of the Calcite. There is a definite curvature to the layers from geologic folding. The embedded Uranophane and Uraninite appear to be integral to several boundaries in the Calcite layers. The deposit of Uraninite and Uranophane that are of crystalographic interest appear to have formed in a fissure between layers. The occurance of these uranium minerals appears to have been from solution without the intervention of a reducing zone from decaying organic matter. Fluorite, as both octahedrons and amorphous masses, can be seen in image 003d. The fluorite is mostly non-fluorescent at both long and short wave ultra-violet light. The Uranium minerals occur primarily in/on two of the boundaries between layers. Both of these occurances are of both Uraninite and Uranophane. There are several relatively large crystals embedded in the Calcite between the two occurence layers. All of the uranium mineralization occurs in a general zone that runs through the center of the specimen. The outer areas of the specimen show little, if any, uranium mineralization. Crystals - Images 003a, 003b and 003d show cubo-octahedronal crystals of uraninite. Image shows a cluster of fluorite crystals growing from one face of the uraninite. Image 003b is an excellent single uraninite crystal of this crystal form. Image 003c shows an intergrown cluster of octahedral uraninite crystals. In all four of these images, Uranophane in the form of rhombohedrons, instead of its usual form of acicular clusters. It can be seen growing together with the Uraninite and appears to have been deposited at approximately the same time. Large crystals of Calcite form the base for the growth of these two uranium minerals. While the Uranophane is the mineral of primary interest on this specimen, the crystalization of the Uraninite is of equal interest. Due to the unusual crystals present, this is a specimen of great interest. Luster - The luster of the Uraninite is sub-metalic. There is considerable surface relief, relative to the size of the crystals. This does not any discernable effect on its sub-metalic luster with the unaided eye. Diaphaneity - The Uraninite is non-transparent, even in its thinest observable sections. Its color is steel black to black.

Specimen #4

Specimen Notes Occurance - The Uraninite in these two images appears to possibly be Uraninite Petrified Wood. The cells in the petrified wood appear to have been well filled with uraninite. See the above notes on uraninite petrified wood. The mineral of interest in this specimen is Rutherfordine (yellow to brown), which appears to be a secondary mineral from the modification of the Uraninite. Matrix - The Uraninite and Rutherfordine occur in a matrix of a soft, powdery, white mineral believed to be talc. The significance of this, and how it may have occurred, is not known.

Specimen Notes This specimen is of silica and uraninite petrified wood. It consists of three general layers: The Zone 1 - the outer layer (inner & outer bark, cambian layer); Zone 2 - the middle layer (sap wood); and, Zone 3 - the center layer (heart wood). These definitions are based on the microscopic examination of the specimen. The Uraninite occurs almost exclusively in Zones 1 and 3, with relatively very little occurring in Zone 2. The density of the wood affects the rate of its decay, and thus affects the strength of the resulting reducing zone that precipitates out the Uraninite. The soft and less dense bark decays very quickly, creating a very strong reducing zone that causes the Uraninite to deposit quickly into a dense structure with only a gross resemblence to the original wood. Silica, as either solid deposits (Quartz) or petrified wood, occurs throughout the specimen. Occurrence - The specimen is stated to be from the "Red Log" Deposit of the La Sal #2 mine. The "Red Log" designation is due to the reddish appearence of the Uraninite when illuminated from certain directions. This red coloration is not obvious under the microscope, though some of the photomicrographic images do show a slight reddish 'cast' to them. Only the areas containing Uraninite show this "Red Log" coloration, the silica petrified wood does not show this coloration. As can be seen on the upper-left side and bottom-center side of image 005b, and the left side of image 005i, the specimen was embedded in quartz sand bonded into sandstone by lime (calcium carbonate - CaCO3). The white areas in images 005a, b and c are all lime or lime-quartz deposits. This type of lime deposit is often refered to in the American south-west as 'Caliche', or hardpan. Other than surface deposits, the lime does not appear to occur within the specimen. In addition to silica and uranium oxide petrified wood, there are small crystaline deposits of both Galena and Quartz. Other minerals do not show themselves, except possibly as coloration of the petrified wood. Zone 1 - Images 005n through 005r are of this zone. Its thickness varies between 0.65 to 1.25 cm. This zone is suspected of being the outer and inner bark, and the cambian layer of the tree. Areas on the outermost surface of this zone have a rough texture that shows no cracking or other breaks. This area may be the surface of the outer bark. The Uraninite in this zone is very dense and highly textured. There is very little indication of cell structure to be found within it, but the overall texture, in cross-section, is similar in appearence to that of the thick bark of some modern trees. The high density and glassy appearence of this zone indicate that it was in rapid decay when the Uraninite was deposited out of solution. The boundary between Zones 1 and 2 is very sharp. As can be seen in image 005n, the Zone 1 material is almost pure Uraninite, while that of Zone 2 is almost pure silica. This is consistant with the difference between the soft cambian layer and harder sap wood layer within a living tree. Zone 2 - This zone is primarily petrified wood consisting of silica. This zone is believed to have been the sap wood layer of the living tree. There is little Uraninite within this zone, most of it being within the rounded nodules found in this zone. Petrified Wood (silica) - Images 005d through 005h concentrate upon the silica petrified wood. Image 005d shows nodules within the petrified wood of what is believed to be a mixture of Uraninite and Quartz (or possibly Coffinite). Due to the alignment and shape of these nodules, and their total lack of texturing typical of petrified wood, it is believed that these are of Uraninite and Quartz deposited within the voids left behind by boring insects. The sub-zone adjacent to Zone 3 has considerable mineralization by Uraninite, discoloring petrified wood from its usual tan color. The boundry between Zones 2 and 3, seen best in images 005i 005j, while not as sharply defined as that between Zones 1 and 2, is well defined by both the the petrified wood being primarily silica on the Zone 2 side, to primarily Uraninite on the Zone 3 side. Additionally, there is a visable change in the cell structure between the two zones. Many a majority of the rounded and elongated Uraninite and Quartz nodules are found adjacent to Zone 1 within this zone. This proximity to what is believed to be the bark and cambian layers of the tree also support the belief that these are insect bore holes within the original living tree. The triangular discoloration in image 005d, just below these nodules, is believed to be the root stub of a branch. This is suggested by its shape, structure, and the structure of the surrounding petrified wood, esspecially in the area to the left of the triangular structure. Galena - The Galena (lead sulfide - PbS) occurs in its cubic form. While not a uranium mineral, its occurance is interesting. Images 005f, 005g and 005h show several of these deposits of Galena. The Galena occurs primarily within a sub-zone 1/3 to 3/4 of the way though Zone 2, near its transition to Zone 3. While the Galena occurs throughout the specimen, it is usually as microcrystals outside this layer. The Galena can be seen to occur within the petrified wood with minimal disturbance to the wood grain. That the grain of the petrified wood is displaced is best seen in image 005h. Even in this image, the Galena has the appearence of occurring with a cavity hollowed out to accomodate it. It is likely that the Galena formed before, or during, the early stages of formation of the petrified wood. The wood displaced by their formation would rapidly decay due to cellular disruption as it was displaced and compressed. In image 005p (also seen in the left center of 005o) is a depression in the Uraninite that has the appearence of having been formed by a Galena crystal, which has since disappeared. Its similarity in appearence to the Galena crystals in 005g and 005h supports this belief. Zone 3 - This zone contains most of the mass of Uraninite, but is a mixture of both silica and uranium oxide. The deeper areas in this zone are of a higher proportion of uraninite. The cell structure of the petrified wood in this zone is considerably courser than that of Zone 2. Image 005j best shows this immediate change in cell structure. The petrified wood of Zone 2 is lighter in color (the Uraninite being more of an impurity), finer grained, and has the cell structures will filled with silica. In Zone 3, the opposite is true, with the most striking being the change from a fine to a course grain. The change in grain occurs as quickly as the change between Zones 1 and 2, though the change in proportion between silica and uranium oxide, and the resultant color change, is not as obvious. Image 005m is taken of an exposed edge of Zone 3 in an area that would have been innermost in the original tree, and at right angles to 005j (looking down from the top of this image in the area being observed). Several areas of this image show not only the wood grain, but the individual cell structures as well. These cross-hatched areas of visable cells are most easily seen along the left edge and lower right corner of the image, but can be seen thoughout the image. The fracture is obviously very uneven, indicating that the uraninite is very dense despite the appearence to the contrary. This high density of deposition causes the resulting petrified wood to not have plane so weakness seen in both natural and petrified wood. Also seen in image 005m are two nodules of glassy material. It is not known if these are Quartz, Uraninite and Quartz, or possibly even Coffinite. As these nodules are of similar general appearence to those in Zone 2, they are likely composed of Uraninite and Quartz filling insect bore holes.   -       -       -

Specimen Notes See notes on Metatorbernite Specimen #2.

Specimen Notes Occurrence - The Uraninite in this specimen occurs a petrified wood. This is common for uraninite found on the Colorado Plateau of the southwestern United States. The dark, silvery gray mineral is Bornite (Cu5FeS4), and the 'white' mineral Calcite. Most of the calcite occurs as Icelandic spar, which shows strong birefringence and is water clear. The Uraninite appears to be either flat or polished black. This is due to the intermix of Calcite with the uraninite. This will be discussed further in the section on Petrified Wood below. Crystals & Birefringence - The only mineral showing a visable crystaline structure is the Icelandic spar calcite. The areas that the birefringence can be seen are those that are cleved into rhomboids or polished into wedges. This birefringence is best seen in images (001c) and (001d). The reflected points of light, particularly in the dark wedge shaped fragment, are doubled vertically (the light is from the top of the image at an approximate 45%#176; angle to the plane of focus. Order of Formation - The birefringence of the Icelandic spar Calcite indicates that its' crystal structure has not been affected, as yet, by the radiation of the Uraninite. As seen in the table of physical properties below, the specimen is quite radioactive. The a-particles are very destructive of crystaline structure, and the calcite is in intimate mix with the uraninite. This would indicate that the calcite is of recent geologic deposition. The 'Peacock ore' coloration of the Bornite is beneith the Calcite, placing its formation prior to that of the Calcite. The Uraninite petrified wood was likely the first to form. Uraninite Petrified Wood - The macroscopic specimen is very dark, from flat black to charcoal gray. This is intermixed with 'white' calcite of the Icelandic spar variety. Examination by eye reveals many areas that have a definate wood-like appearence, hinting that the Uraninite was deposited into decaying wood. Compare this with Specimen #5 above. Microscopic examination of the polished surface at first does not show any cellular or wood grain structure. However, examination of the black shallow 'U' shaped structure reveals many open cells of wood petrified by Uraninite. This confirms that the visual impression of petrified wood is accurate. The cells are filled with calcite, which being transparent, gives the appearence of a solid black mass when the Uraninite petrified wood is not polished to a thin section. With the Uraninite reflecting little light back, and the Calcite being completely clear, the impression of a solid black mass of Uraninite is given. Bornite - The Bornite shows considerable variation in texture and the shade of gray it presents. Most of this variation in the darkness of gray is due to the polishing, which presents many very fine scratches that can cause an increase in reflectance at certain angles of illumination. The most common appearance is a gray associated with a freshly broken cast iron surface. The Bornite appears in two general forms: solid masses, as seen in (007e); and long dendrites, sometimes branching, as seen in (007f). There are two forms of dendrites, as can be seen in (007f): long, smooth parallel deposits (right side of image); and long deposits with many side branches that tend to intergrow (left side of image). With the knowledge that the Uraninite replaced wood, it is believed that the wood grain structure of the Uraninite caused the Bornite to be deposited along the course growth grains of the original wood, giving the long, parallel structure it has. Images (007f) and (007g) give the appearence that the Uraninite may be converting to a secondary Uranyl mineral. However, the upper left corner of (007h) and all of (007i) show the golden color that gives Bornite its common name of 'Peacock ore.' While it is possible that a small amount of the Uraninite may have been oxidized to a uranyl mineral, it is more likely that the colors seen are due to oxidation of the Bornite, which was then coated by the Calcite. Luster - The polished surfaces of all three minerals have a glassy luster. The unpolished Uraninite varries from flat black, as if coated with carbon soot, to a polished, textured surface where the visual appearence of a wood grain is apparent. Beneith the Calcite, the Uraninite presents a flat black appearence. Even the open cell structures of Uraninite embedded in Calcite, seen in (007b), appear to be a flat black. The Bornite has the luster of polished cast iron of high carbon content (dark gray with a lot of surface texture). On the unpolished surface of the specimen, the bornite appears black to charcoal colored. It is not easily differentiated from the Uraninite, and shows no 'Peacock ore' coloration - no oxidation.   -     Specimen Physical Properties Weight: 103.40 grams     Dimentions: 4.1 × 4.1 × 2.2 cm   (one side polished) g-Radiation Level (2.5 cm): 2491 cpm 2.49 msieverts background: 36 cpm

 

Specimen Notes See notes on Carnotite Specimen #1.