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Norman King's Photo Gallery

G6W-G97Agate (Var: Crazy Lace Agate)

Multiple photos available
Sierra Santa Lucia, Ejido Benito Juarez, Mun. de Ahumada, Chihuahua, Mexico

Field of View: 2.0 mm

This composite photomicrograph shows two views of a thin section of crazy lace agate from Sierra Santa Lucia, the classic locality for crazy lace agate. The left view was taken using cross-polarized light, and the right view is in plane-polarized light. This makes it clear why we use cross-polarized light to study chalcedony in thin section. Shown here is a chalcedony spherulite that is more complete and more attractive than most. The spherulite is 0.62 mm in diameter. (FOV is 2.0 mm per side). The central portion of the spherulite consists of radiating fibrous microcrystals of quartz. In fact, any such radiating mass of translucent fibrous crystals will produce a pseudo-interference cross such as this, caused by the arrangement of the polaroid plates, or "nicols," at 90 degrees to each other. The daughter photo shows a second spherulite only about a centimeter away from this one, but a long distance in terms of the history of that portion of the rock, resulting in notably different spherulite structure. Crystal spherulites are like snowflakes–their overall structure may be similar, but details differ so that no two are identical, just like all crystals and crystal groupings of any mineral are different. Collection, thin section, and photomicrographs by Norman King
Copyright: © Norman King      Photo ID: 929955     Uploaded by: Norman King   View Count: 27   Approval status: Public galleries    Type: Photo - 2035 x 900 pixels (1.8 Mpix)

3K6-YGLAgate (Var: Crazy Lace Agate), Muscovite

Sierra Santa Lucia, Ejido Benito Juarez, Mun. de Ahumada, Chihuahua, Mexico

Field of View: 2.1 mm

Detail of chalcedony matrix of the agate in thin section using cross-polarized light. This matrix has no special features in itself, but includes numerous crystals of muscovite, perhaps the variety called illite. These are made clear in this view by second-order blue interference color, but are obscured somewhat by being associated with darker “dirty” areas that are relatively rich in material other than microcrystalline quartz. Most in-depth published discussions about chalcedony I have seen mention that fine phyllosilicates (often referred to as “clays”) are likely mixed with chalcedony as accessory minerals, but I have not seen any photomicrographs published to illustrate that claim. So, here is the proof! Electron micrography might also reveal presence of fine micas, but can only show form (habit) of minerals. In this field of view (2.1 mm) the muscovite crystals range from 0.005 to 0.06 mm (5 to 60 microns). The largest example is near middle of slide at far right. Collection, thin section, and photomicrograph by Norman King.
Copyright: © Norman King      Photo ID: 929946     Uploaded by: Norman King   View Count: 7   Approval status: Public galleries    Type: Photo - 1280 x 960 pixels (1.2 Mpix)

The Great Unconformity at Siccar Point

Multiple photos available
Siccar Point, Scottish Borders, Scotland, UK

Siccar Point is arguably the single most important outcrop in the history of geology, but the site and its significance is not well-known to locals (I found out!), and is not well marked on location. Nevertheless, this is where James Hutton (1726-1797) and companions including geologist Sir James Hall and mathematician John Playfair discovered a striking exposure of the “Great Unconformity,” a feature that convinced Hutton that Earth history included great cycles of deposition of sediments in the sea in the same manner as we can see them being deposited today, followed by lithification and uplift of the resulting rocks, which were then eroded, and covered again by the sea, when the sequence was repeated–again and again. Hutton’s work has been credited with marking the beginning of uniformitarianism and making geology a true observational science.
Copyright: © Norman King      Photo ID: 929595     Uploaded by: Norman King   View Count: 21   Approval status: Public galleries    Type: Photo - 2344 x 1796 pixels (4.2 Mpix)

389-HLDAgate (Var: Crazy Lace Agate)

Sierra Santa Lucia, Ejido Benito Juarez, Mun. de Ahumada, Chihuahua, Mexico

Field of View: 5.4 mm

Thin section in cross-polarized light showing a tiny segment (FOV = 5.4 mm) of crazy lace agate from the classic locality in Chihuahua, Mexico. At this site the botryoidal chalcedonic layering broadened to go around a cluster of spherulites that are not present within thinner layering on either side. The scattered opaque smudges are either iron or manganese oxides, and the straight objects at upper left may be rutile crystals that came loose from their “roots.” Each spherulite in the cluster exhibits a Maltese cross with blue-white background. Collectively, these suggest a fireworks display performed to celebrate New Year’s Day. Thin section, photomicrograph, and imagination by Norman King. Happy 2019!
Copyright: © Norman King      Photo ID: 929335     Uploaded by: Norman King   View Count: 23   Approval status: Public galleries    Type: Photo - 2000 x 1500 pixels (3.0 Mpix)

XDP-3KKQuartz (Var: Chalcedony)

Multiple photos available
McNamara, Missoula Co., Montana, USA

Field of View: 2.7 mm

Thin section of chalcedony using cross-polarized light. The lower part is dominated by basic chalcedony spherulites, each composed of four subdivisions divided by a dark Maltese cross, often referred to as a pseudo-interference figure. Where crowded together, however, the spherulites are more rectangular than circular. The arms of the Maltese cross (which is known by several other names, including Norman cross) are produced by extinction directions in the petrographic microscope, and all of them are always oriented “north-south” and “east-west” regardless of the position of the microscope stage. Chalcedony in spherulites ranges in color from white to gray, with yellow to orange in the thicker portions. Some of the spherulites higher in this view have become greatly extended upward above the east-west arms of the cross, developing a plumose habit mostly above that level. This habit is produced by extensive Brazil twinning on a "micro" scale (see Heaney, 1993, Fig. 3). The feather-like plumes are more colorful upward, showing first-order yellow, orange, and red, and then second-order violet and blue. Some of the plumes reach completely across the remaining portion of the chalcedony field. Based upon the appearance of this habit in thin section, I call it (facetiously) “hair-on-fire chalcedony.” Daughter photos show other examples in the same specimen to show the range of appearances. Thin sections made by Norman King from material collected by Daniel Bennett and now in King’s collection.

Ref.: Heaney, P. J., (1993) A proposed mechanism for the growth of chalcedony. Contributions to Mineralogy and Petrography. 115: 66-74.
Copyright: © Norman King      Photo ID: 929139     Uploaded by: Norman King   View Count: 15   Approval status: Public galleries    Type: Photo - 1036 x 930 pixels (1.0 Mpix)

C57-1JXChalcedony (Var: Fire Agate)

Multiple photos available
Aguascalientes, Mexico

Field of View: 9.1 mm

We need to know what is eating our rocks and minerals! This thin section in cross-polarized light shows endolithic fungi or flora (red algae) extending a few millimeters into chalcedony from an opaque rocky substrate at bottom. The tubular filaments and chambers are undoubtedly connected by filaments outside the plane of the thin section. In this case, note that chalcedony formed around the biologic structures. My interpretation is that the rock was opaline when initially bored by the endoliths, and then the opal was replaced by spherulitic (botryoidal) chalcedony. Biologists and engineers are very interested in this kind of “weathering” of man-made and natural structures in both terrestrial and marine environments. See daughter photos for overview of the hand specimen and thin section, plus enlarged views showing more details. Collection, thin section, and photographs by Norman King.
Copyright: © Norman King      Photo ID: 927917     Uploaded by: Norman King   View Count: 24   Approval status: Public galleries    Type: Photo - 2000 x 1500 pixels (3.0 Mpix)

HFG-JXVChalcedony (Var: Agate), Rutile

Sierra Santa Lucia, Ejido Benito Juarez, Mun. de Ahumada, Chihuahua, Mexico

Field of View: 13 mm

Thin section in plane polarized light showing needles of rutile within crazy lace agate from the classic locality. Note that agate coats the rutile needles, forming projections much thicker than the needles themselves. Identification of rutile based upon habit and association. Collection, thin section, and photomicrograph by Norman King.
Copyright: © Norman King      Photo ID: 927562     Uploaded by: Norman King   View Count: 23   Approval status: Public galleries    Type: Photo - 1280 x 960 pixels (1.2 Mpix)

PFF-2UCOpal

Multiple photos available
Milford, Escalante Desert, Beaver Co., Utah, USA

Field of View: 18 mm

Two views of the same area of “bacon opal” in thin section. The daughter photo is the slabbed hand specimen with an outline showing the area covered by the thin section. You need to see the daughter photo to see why it is called bacon opal. The left view of the thin section was taken in plane polarized light, and the right view was taken using cross-polarized light. Note that the right view is almost completely dark. When cross-polarized light passes through a mineral in thin section it usually produces bright interference colors and perhaps other interesting effects. This is not true for opal, because opal is not really composed of minerals. Opaline material lacks a crystal lattice, and without a crystal lattice no cross-polarized light can pass through it. Like white light, plane-polarized light does pass through the material, so the left view shows the bacon-like banding of the opal, albeit without color. In the right view, only a little light passes through the opal where bands are strongly curved to make features resembling the botryoids of chalcedony. Those are where incipient crystallization has apparently begun. I do not know what mechanism favors crystallization at those places. If anyone else knows, please send me a personal message, perhaps with a reference I can look up and you won’t have to spend a lot of time on me! Collection, thin section, and photograph by Norman King. Locality information available on the web is inconsistent, but this material closely resembles “bacon opal” and “candy-stripe opal” reported from near Milford, Utah (apparently several miles NE of Milford). FOV is 18 mm for each side.
Copyright: © Norman King      Photo ID: 927401     Uploaded by: Norman King   View Count: 9   Approval status: Public galleries    Type: Photo - 1853 x 1222 pixels (2.3 Mpix)

MPD-696Quartz (Var: Chalcedony)

Giverny, Eure, Normandy, France

Field of View: 2.0 mm

Thin section of chert from cream-colored nodule (inset at lower left; coin is 19 mm in diameter) from Cretaceous chalk at Giverny, France. Fragments of such nodules are abundant in road cuts through weathered chalk in town. The chert is composed of millions of microcrystals of quartz (var. chalcedony). This specimen includes several fossil fragments in the field of view, many of which appear to be needle-like siliceous sponge spicules. Skeletons of siliceous organisms including sponges and radiolarians are often cited as possible sources of silica that precipitated to form chert nodules after deposition of the chalk. A light brown piece of skeletal material at upper right may be phosphatic vertebrate material which would be similar in color.
Copyright: © Norman King      Photo ID: 924506     Uploaded by: Norman King   View Count: 10   Approval status: Public galleries    Type: Photo - 1280 x 960 pixels (1.2 Mpix)

XCA-HYYQuartz (Var: Chalcedony)

Giverny, Eure, Normandy, France

Field of View: 2.5 mm

Thin section of chert from black nodule (inset at lower middle; coin is 19 mm in diameter) from Cretaceous chalk at Giverny, France. This rock might also be called flint, but it shows nothing to support a different name than lighter-colored chert specimens from the same locality. The chert is composed of millions of microcrystals of quartz (var. chalcedony). Fragments of such nodules are abundant in road cuts through weathered chalk in town. Note the prominent siliceous microfossil of a planktonic radiolarian at lower left. Another inset (above left) shows a line-drawing of a similar fossil that is not exactly the same, but close. Siliceous fossils of radiolarians and sponges are often cited as possible sources of the silica that precipitated to form chert nodules after deposition of the chalk.
Copyright: © Norman King      Photo ID: 924505     Uploaded by: Norman King   View Count: 9   Approval status: Public galleries    Type: Photo - 1280 x 960 pixels (1.2 Mpix)
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