Specimen Notes
Image Note - Image (001a) is produced from four images using a modified CombineZ4.0 combing program. This produces a synthetic depth of field of nearly 1 cm.
Occurrence - The Meta-Autunite appears to occur on limestone that is incompletely converted marble. In addition, areas of the pinacoid faces of the Meta-Autunite have a very light druse of extremely small acicular crystals with sharp terminations. It is not known what mineral these needles are, but they have the appearance of Uranophane, which is not known to occur at the Daybreak mine.
Crystals - The Meta-Autunite of the entire specimen is crystaline, except where the specimen was mounted to a lucite plate, where the glue appears to have dissolved some of the Meta-Autunite. Almost all crystals are pseudomorphs of Autunite, and are partial due to contact with other crystals or the matrix.
The Meta-Autunite is in two colors, yellow-green and dark green. The dark green portion appears to be very dense with no striations characteristic of meta- transformation (water loss). The dark green mineral also shows no internal fracturing along the {001} plane (see images (001c) and (001d)), as does the yellow-green portion of the mineral. In image (001e) is shown a corner of a crystal whose edge is yellow-green for approximately 0.8 mm inward from the edge. Image (001f) is a close-up of that corner. From there, it turns into the dark green mineral. This is characteristic of minerals transforming into their meta- form. It is believed for these reasons that these darker areas may be Autunite, which also occurs at the Daybreak Mine.
The belief that the dark green mineral may be Autunite undergoing meta- conversion is furthered by another observation. The dehydration appears to be occurring from the edges inward, indicating that there is a preferential direction within the crystal structure for water loss. Areas away from the edges that have become Meta-Autunite often show deep fractures or cleavages within or at an edge of the converted area. However, images (001c) and (001d) do show fractures and cleavages that are not associated with meta- conversion. These areas' cleavages may be due to twinning.
Twinning - In the lower right quadrant of image (001c) can be seen a cleavage that appears to be along a plane of reflective twinning. The {100} and {010} cleavage planes seen in (001g) are likely due to a strong appearance of pseudocells, oriented at 45° to the normal unit cells, are seen with · 3H2O Meta-Autunite. A kind of pseudo-twinning may be occurring due to the presence of these pseudocells. The plates along the left and bottom-left edges of image (001g) also suggest this very strongly. Image (001c), and the magnified view of the same area in (001d), show similar cleavages that also indicate a form of pseudo-twinning, beyond the reflective twinning already mentioned.
Cleavage - In image (001b), the 'cocks comb' stack of what were once Autunite crystals are shown to be cleaved along the {001} plane into stacks of plates. When this image is examined more closely, these plates are often seen to be further cleaved into still thinner plates. This shows the micaceous habit of the Meta-Autunite.
The surface striations and cracks occur along the {110} planes. One plane is considerably favored for these striations and cracks than the other in many areas. These same planes show a weaker cleavage that also parallels the prefered direction of the striations. This suggests that the Meta-Autunite crystal may not have a true tetragonal crystaline structure. This may be due to possible twinning of the crystals.
Additionally, minor striations along the two {100} and {010} planes (45° diagonal) are seen to occur. Fractures along this same plane, seen in images (001c) (001d), and (001g) can be seen. The cleavage in the first two images appear to have been caused by pressure from adjascent crystals growing against the imaged crystal, possibly during the growth of the original Autunite. In (001g), the cleavage along the {100} and {010} planes very pronounced, and is likely due to shrinkage of the Autunite as it became Meta-Autunite. In all of these images, the convertion to Meta-Autunite appears to be still ongoing.
Appearence - The Meta-Autunite is in the form of a pseudomorph of Autunite in 'cock's comb' stacks of crystals. Mentally eliminating the fractures, these can be seen to be stacks of Autunite crystals (see image (001c) above).
Diaphaniety - The crystals are poorly translucent at the macroscopic scale, but under the microscope become more nearly transparent. This can be seen in all the images as being primarily due to scattering of light off of surface striations and internal fractures caused as the Autunite lost water and became Meta-Autunite.
Luster - The luster is henerally adamantine, though several areas do present a somewhat resinous luster.
Color - The color of the Meta-Autunite is its typical yellow-green. Areas of darker green occur. These areas have little or no fracturing or striations from water loss. This makes them appear more solid than the yellow-green mineral, furthering the belief that they are likely Autunite that is converting over. Image (001e) shows a corner of a crystal where the edge is yellow-green for approximately 0.8 mm inward, where it turns into the dark green mineral.
Fluorescence - Under long wave ultraviolet light, the yellow-green mineral fluoresces a bright yellow-green very stongly. The dark green mineral fluoresces very weakly, if at all. Due to the close proximity of the highly fluorescent yellow-green mineral, the dark green mineral may be simply reflecting this fluorescence.
Under short wave ultraviolet light, the specimen fluoresces much more stongly. The dark green mineral also fluoresces, but considerably weaker than the yellow-green. The central areas of the dark green mineral fluoresce the most weakly of all.
Specimen Physical Properties
| Size (excluding mount): |
2.7 cm |
2.7 cm |
1.7 cm |
| Weight: |
23.49 grams |
|
includes lucite mount
(3.1 x 3.2 x 0.8 cm) |
| g-Radiation Level: |
1388 cmp
(30 min. average);
(1340/1437 spread) |
1.388 msieverts |
background: 22 cpm |
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