Agate Historical Tales.
Agate, jade, also comes from the Western Regions. The arts and sciences are intertwined, and there is a horse's brain, so its people are named after it. This is the description of agate by Cao Pi, Emperor Wen of Wei of the Three Kingdoms, in "Agate Le Fu (and Preface)", and the author also praised it like this: "The brightness of the five colors of the bud is matched with the streamer of the bright sun." ”
Silk-wrapped agate slice ornament, collection of the Geological Museum of China Photo by Guo Keyi.
As a product of natural action, agate has been loved by emperors and literati since ancient times for its gorgeous color, beautiful ornamentation and a wide variety of varieties. Agate is a beautiful sacred stone carefully crafted by nature, how many kinds of agate are there? How are its unpredictable stripes formed? Can modern artificial technology make them "beautiful"?
Classification of agate.
As the saying goes: "A thousand kinds of agate and ten thousand kinds of jade." "Agate is not only colorful and diverse, but also has a long history and a wide range of origins, so it gives people a sense of variety. Usually, agate can be divided into varieties such as white agate, red agate, blue agate, green agate, purple agate, yellow agate, and black agate according to its color difference. The band-like structure is the biggest feature of agate, and its ribbon can be both multi-colored and homo-colored, and has subtle differences in color, hue, width, transparency, shape, etc., and the appearance is also ever-changing. Therefore, in this paper, agate is subdivided into 14 subspecies according to the color combination and morphological characteristics of the stripes, special optical effects, special shapes and pattern decorations.
Above: Tubular agate slices, collection of the Senckenberg Museum of Natural History, Germany Photo by Lu Linsu; Bottom: Dendritic agate ring face, collection of the Geological Museum of China Photo by Guo Keyi.
Silk agate is a monochrome agate with a red (brown) color or stripes with white or black. It is usually red (brown) white or red (brown) black, and the bands are clear and straight, suitable for making two-tone relief and intaglio artworks. Sometimes, people confuse it with onyx, but onyx is just a black and white agate, while silk agate is mainly a red and white agate, with occasional red and black variants. The ribbon-like pattern it possesses is also one of the important features that distinguishes it from onyx. Winding agate is mainly produced in India, the United States, the Czech Republic, Madagascar, and also in Xinjiang, China.
Filament slices with sand core, collection of the Senckenberg Museum of Natural History, Germany Photo by Lu Linsu.
Onyx is a monochrome agate with black and white, straight stripes, that is, true onyx or Arabic onyx, sometimes referred to as black onyx. It has a low transparency and is suitable for two-tone reliefs – a combination of a black base and a white cover – and is produced mainly in the Brazilian states of Pará and Minas Gerais, India**, the Argentine province of Catamarca, Madagascar and Uruguay, as well as in Mexico, Romania, Afghanistan, Australia, Russia, the United Kingdom and the United States.
Castle Agate gets its name from the pattern it presents on its exterior. When the thin layer in the castle agate takes on a pointed outline, its pattern resembles the fortress of an ancient castle. The agate can be found in the Juken quarry near Ida Oberstein in Germany and in the porphyry and rhyolite of the Polish province of Lower Silesia.
The eyeball-like agate has an annular striation arranged in concentric circles or eccentrics around a center. One example of this is the eye agate, which has a black heart and displays a concentric layered pattern around the black heart, resembling an eye.
Polygon agate, as the name suggests, is an irregular polygon, because it was found in large quantities in the Brazilian state of Paraiba in the 70s of the 20th century, also known as Paraiba agate. It is also found in places such as the Rhineland-Palatinate in Germany.
Above: eyeball-shaped agate slice ornament, RAND Vertical Cultural Development (Beijing) ** Collection; Bottom: Onyx Ball Photography by Chen Duaneng.
Tubular agate is an agate containing a large number of tubular bodies, and the openings of the tubular bodies often have concentric bands with clear borders, mainly produced in Ida Oberstein, Germany, and also in the northeastern Middel of Morocco.
Water urchin agate is a thin-walled agate or monochrome chalcedony nodule with a large cavity inside and water sealed. When shaking, the sound of water can sometimes be heard. But the water in the agate will spill out through tiny "capillaries" and evaporate from the surface, slowly drying out. It is mainly produced in Brazil and Uruguay, and is also produced in Fuxin, Liaoning Province and Xunke, Heilongjiang. In 1978, a giant water urchin agate weighing 32,400 grams was produced in the Sunk area; In 1986, Heilongjiang Province Qiqihar Jade Factory also successfully carved a piece of China's largest water urchin agate work - "Grand View Garden", weighing 7,350 grams, of which the volume of water urchin is more than 1,100 cubic centimeters, and stored about 850 grams of clear water, rare and rare, can be called "rare national treasure".
Dendritic agate is a translucent, colorless or white chalcedony or agate containing contrasting branched or dendritic inclusions (actually brown or black iron or manganese oxides). It is mainly produced in countries such as Brazil, Canada, India, Iran, Kazakhstan, and the United States.
Halo agate refers to the sub-transparent to translucent agate with halo effect, also known as rainbow agate. This is due to the fact that the agate stripes are extremely fine – consisting of alternating layers with a slightly higher and lower refractive index, arranged in parallel and regular patterns, with high transparency, and superimposed on a regularly arranged band of agate wall lining that acts as a diffraction grating. When it is cut into thin slices or carved into unique carvings, under transmitted light**, it produces a spectral color due to interference, resulting in a rainbow-like effect. It is one of the most prized varieties of agate and is mainly found in the Brazilian state of Rio Grande do Sul, followed by the states of California, Tennessee, Texas, Oregon, and New Mexico in the United States.
Fire agate is a thin, subtranslucent to opaque layer of chalcedony with a halo on a brown, red to orange background. Due to the grape-like aggregate composed of goethite or limonite flakes inside it, it diffracts and interferes with light, resulting in a halo effect or "fire". It is mainly produced in countries such as the United States and Mexico.
Fire agate drop-shaped pendant, collection of the Geological Museum of China Photo by Guo Keyi.
Grape agate refers to the appearance of grape-like agate beads assembled into agate, because of its unique shape, the whole body is full of colorful colors (mostly light red, purple, dark purple, green and other colors), different sizes (as large as grapes, small as pearls or even millet), various forms (bead-like, ball-shaped or drop-shaped), natural bead-shaped agate balls, like a bunch of grapes, hence the name. It was first discovered in the 80s of the 20th century near the Suhongtu crater of the Alxa League in the Inner Mongolia Autonomous Region of China, and the grape agate on the market today mainly comes from Indonesia.
Purple grape agate, produced in Indonesia. ** By thecollector'S Edge offers.
Feathery agate refers to agate with a feathery or cloud-like pattern, also known as cloudy agate. Its white streaks are usually outlined by the tips of clear and transparent quartz crystals, essentially a mixture of negatively ductile chalcedony and n-chalcedony. This is one of the most popular agate varieties by the Olympic Organizing Committee. It is found in places like Rio Grande do Sul in Brazil.
Moss agate is a translucent chalcedony containing fine scaly green hornblende or chlorite inclusions that aggregate into a moss pattern, also known as moss agate. Sometimes it can also show brown and red patterns, which is due to the presence of iron oxides in hornblende or chlorite. This type of agate is mainly produced in Oregon, Wyoming, Montana, Texas and other states in the United States and Washington, D.C., and is also produced in Gascotia, Canada, Tavush Province of Armenia and Hefs County, Hungary, and is also produced in India, Australia, Iran and other countries.
Landscape agate refers to chalcedony that contains traces of other mineral impurities that cause different color combinations to form a landscape pattern. Cuba produces brown and blue scenic agate, and the most famous scenic agate on the market today is the "marine chalcedony" from Madagascar.
Strips of agate.
Banding is the most distinctive feature and visible property of agate. The structural characteristics of these bands indicate that the formation of agate is not a continuous process, but consists of several steps: as the lava slowly cools, the later silicon-rich hydrothermal fluid will slowly enter the stomata along the cracks created by the cooling contraction of the precipitated chalcedony layer, and precipitate in the form of diffusion and gelatinity, forming banded chalcedony. It was found that the bands of agate can be distinguished into 2 typical types: wall-lined bands and horizontal bands.
Wall-lined bands are characterized by the orientation and growth direction of individual bands perpendicular to chalcedony fibers (in fact, "virtual fibers"). As chalcedony fibers grow from the cave wall to the cave, concentric onion-like patterns are formed, and these concentric layers follow the shape of the cave wall. In addition to the visible wall lining bands, agate also has a combination of different trace elements and hydroxyl concentrations on the micron scale. Bands of wall lining are not confined to the walls of the geode, and similar bands form around other structures that grow into the cav, such as crystals or mossy inclusions. An interesting phenomenon can also be seen at the base of the agate, namely that the ribbon pattern is not symmetrical, and the fibers are not perfectly straight, but curved towards the oldest wall lining bands.
The perimeter of the agate slice is a wall lining strip, and the lower left is a horizontal strip in the collection of the Senckenberg Museum of Natural History, Germany
Horizontal bands are not very common, as they were first described in Uruguayan agate, also known as "Uruguayan bands". It is commonly found in "thunder eggs" in acidic volcanic rocks such as rhyolite and is often accompanied by wall-lined bands. However, in terms of the geometry of the horizontal band, its properties and origins are different from those of the wall lining band. In geodes, horizontal bands are made up of small, irregularly spaced layers of small, irregularly spaced chalcedony spheroids, sometimes accompanied by the formation of quartz crystals. The horizontal strip can be used as a level gauge to determine the original orientation of the sample in the surrounding rock. When translucency or color differences between two layers are significant, agate with horizontal bands can be used to engrave two-color reliefs.
Optimized treatment of agate.
Some of the agate we see is not pure and natural, but has been artificially optimized. These agates are filled, heat-treated, and dyed to achieve the desired color.
Agate is a slightly porous material, which is due to the fact that the individual crystallites in the fibers are not as tightly connected to each other, making it easy to stain. When agate is artificially dyed, the color penetrates much faster in a direction parallel to the fibers, which are mainly perpendicular to the band structure rather than distributed along the agate layers. Before dyeing, agate lacking bright colors and stripes is sawn or sliced, preheated, and artificially "enhanced" with various dyes to produce black, green, blue, yellow, purple and red for gemstones. Dyed agate is intensely colored, and its color distribution is uneven under magnifying glass, which is mostly enriched in fissures, intergranular crevices, or surface depressions, which is also an important feature of identification.
The agate bracelet and necklace filled with "Nanhong" behave differently under natural light (above) and ultraviolet light (below), and those with chalky orange-red glow under ultraviolet light indicate that they have been glued with glue Photography Li Ting.
In addition to dyeing, heat treatment is also a way to optimize agate. Under natural conditions, an oxide containing iron and presenting a dirty yellow or light yellowish brown agate can be heated to obtain a beautiful reddish-brown color. At present, the vast majority of reddish-brown agate on the market is obtained by heat treatment, commonly known as "burnt red" agate. Since heat-treated agate is not easy to detect, and dyed agate has a long history and is widely accepted, they are all optimized, so this is also a common method of counterfeiting for some "southern red" agate.
Generally, colorless oil and wax are commonly used to fill the gaps of agate, or a small amount of resin to fill the gaps of agate to slightly improve its appearance, which is an optimization. If a small number of cracks and voids in agate are filled with glass or artificial resin to improve its durability and appearance, although it is still an optimization, it must be noted. However, if porous and multi-fissure agate is infused with cured materials such as lead glass and artificial resin to change its durability and appearance, it is a treatment. There are four ways to identify the filled agate: one is to magnify the inspection, which shows that there is a difference between the surface gloss of the filled part and the main agate, and bubbles can be seen in the filling; Second, under long-wave and short-wave ultraviolet light, there is a difference between the fluorescence of the filled part and the main agate; the third is the infrared spectroscopy test, which can see the infrared absorption band of the filling; Fourth, luminescence image analysis, which can see the distribution state of the filling.
Stained agate slices, photographed with horizontal bands Lee listening.
From ancient times to the present, people have been flocking to agate, and collecting and wearing agate is also a symbol of identity and status. The reason why agate is beautiful and colorful is the result of hundreds of millions of years of geological processes. Today, with artificial methods, we can make it look more beautiful, but we must also beware of falling into the trap of commercial fraud and not letting the beauty be dusted.
*: Earth Magazine.
Edit: Unit 7.
*The content represents the author's views only.
It does not represent the position of the Institute of Physics of the Chinese Academy of Sciences.
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