What is the difference between agate and chalcedony?

Waxy or matte shine. Hardness 6,5-7. Specific gravity 2,58-2,64 g/cm3. Chalcedony has different colors, various combinations of colors and shades. It can be smoky, bluish, milky gray, bluish-black, yellow, red, orange, brown, brown, green, apple green, green with red spots, black with white, brown with white, red with white, scarlet is unique chalcedony. Often faintly translucent. Doesn’t give a damn. There is no cleavage. The fracture is flat-shelled. Often produces sharp cutting edges when fractured. Swelling, dense; Sometimes small quartz crystals are observed in the voids. Amorphous. It also produces pseudomorphs of other minerals (calcite) and organic remains (wood and shells).

Features. Chalcedony is distinguished by its waxy luster, great hardness (leaves a scratch on glass), lack of cleavage, and dense structure. It differs from quartz and other similar minerals in luster. Chalcedony looks like frozen jelly.

Chemical properties. Insoluble in acids (except for HF).

Varieties and photos of chalcedony

• Cornelian (carnelian)—red.
• Sarder – brownish-brown, red when exposed to light.
• sapphirine – milky blue.
• Chrysoprase – apple green, bright.
• Plasma – onion green.
• Heliotrope – heterogeneous, dark green, slightly transparent with dark red spots.
• Moss chalcedony – different colors with patterns or inclusions reminiscent of moss. Chalcedony patterns can be concentric, plane-parallel and more bizarre – mossy, ocellated, cloudy, star-shaped, landscape.
• Variably colored concentrically folded chalcedony is called agate.
• Chalcedony contaminated with impurities (clay, opal, calcite, etc.) is nicknamed flint. The color of flint is brown, yellow, gray, black; opaque. Flint is found in the form of nodules, mainly in limestones, marls and chalk.

Sapphirine. © Simon Egester Chrysoprase Heliotrope. © Adam Ognisty Flint. © Adam Ognisty

Sometimes agate is transparent with thin layers, less often yellowish and brownish in combination with white and smoky color, and very rarely pink.

Varieties and photos of agate:

1. Onyx – alternating black and white layers (sometimes onyx is called agate with a plane-parallel structure).
2. Sardonyx – brown-brown and white layers.
3. Carnanol onyx – brown and black layers.
4. Carneolonyx – red and white layers.

Onyx. © Rob Lavinsky Carneolonyx Sardonyx. © Rob Lavinsky

Origin

Chalcedony is released from aqueous solutions in the form of deposits and kidney-shaped formations in volcanic rocks. Fills voids in erupted igneous rocks (basalts, traps, porphyrites), occurs in the form of interlayers and veinlets among rocks, is part of metamorphic rocks (jasper), sedimentary rocks (opoka); in addition, it is found as a fringing substance of shells, plant remains and forms crusts on the surface of sedimentary rocks; also found in placers (pebbles, boulders).

Often forms characteristic concretion forms, cement in sandstones, and replaces fossils. It is found in the voids of igneous rocks, in limestones, replacing quartz, in diatomites, replacing opal. Chalcedony is also formed as a result of chemical weathering of silicates, such as orthoclase.

Chalcedony is also found of non-volcanic origin. It forms in limestone voids. The most popular are flints from Moscow region: Dmitrov, Gzhel, etc.

Satellites: quartz, opal, limonite, carbonates.

Applications of agate and chalcedony

Chalcedony is used as a polishing material, agate is used to make souvenirs and jewelry (brooches, bracelets), agate mortars are used in the chemical industry; They also produce prisms for precise chemical balances, parts for electric meters, and manufacture watch cases, compasses, electric meters, balls for bearings, and prisms. Agate is used for processing hard metals, in precision instrument making, and during drilling operations. Agate is a highly acid-resistant material.

Place of Birth

Chalcedony deposits are confined to areas where volcanic basalt eruptions occurred in the geological past. They are known in the Caucasus, the Urals, Chukotka, Kamchatka, the Commander Islands, Eastern Siberia, Transbaikalia, Northern Timan, near Magnitogorsk, and Karelia. The deposits of technical agate – Akhaltsikhe are located in Georgia. A large agate deposit is located in the Izhdevan and Mzhaven regions of Armenia. There are also agate deposits in the Crimea (Kara-Dag), Semirechye (Kazakhstan), and the northwestern spurs of the Tien Shan. Chalcedony and agate are found in Taimyr, Kolyma, Chukotka, and Kamchatka. Suchan agates (Far East) are beautiful. Colored agates are found in Transcaucasia. In the river basin Nora in the Amur region, a rich treasure trove of agate was discovered. Carnelian is mined in Chukotka; it is also known in the Magadan region. Chrysoprase is also mined in South Australia. In the Orenburg region, chalcedony is found in the weathering crusts of serpentenites (Aiderbak, Akkerman and Buruktal nickel deposits, Kiembaevsky asbestos quarry).

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This is the name of a variety of chalcedony, which represents layered-striped intergrowths or a spotted mixture of variously colored, transparent and opaque, varieties of chalcedony, sometimes with an admixture of jasper, carnelian, quartz, amethyst and other forms of amorphous and crystalline silicic acid. Agate consists of pure silicic acid with a small admixture of iron oxide. It occurs in the form of tonsils and spherical aggregates that fill pores and voids in more or less decomposed volcanic rocks, mainly in melaphyres. Large spherical and shaped nodules in the center often contain druses of amethyst or calcite. Agate is a mineral of aqueous, hydrochemical origin, formed by deposition on the walls of pores and voids of concentric layers of amorphous silicic acid from solutions containing it.

The variously colored layers of agate are extremely delicate and often so thin that Brewster could count 17000 of them on a piece one inch thick. Agate exhibits an extremely wide variety of colors and patterns; Most often it is translucent or even transparent, but in places it is opaque, layer-by-layer colorless or colored white, reddish, orange, brown, purple or blue. By the nature of the arrangement of differently colored layers and the pattern they form, several varieties of agate are distinguished. Thus, agates with a stripe-like arrangement of different layers are called “band agate”; often the stripes represent acute-angled bends and resemble, as it were, the plan of a fortress: this is fortress agate; in addition, they also distinguish between spectacled, dotted, coral, conchoidal, mossy (from the pattern formed by chlorite inclusions), cloudy, etc.; finally, breccia-like agates are called agates consisting of angular fragments of agate cemented with amorphous silicic acid or, for example. at Schlotwitz in Saxony, with amethyst.

Some agates show rainbow colors in transmitted light and are therefore called “rainbow”. Agates also include striped onyx or sardonyx, consisting of black, red and milky white, often artificially colored stripes; Onyx has been a favorite material for artistic cameos since ancient times. The hardest varieties of agate are used for various crafts, such as jewelry, mortars and pestles, rings, cups, buttons, etc. In physical instruments, agate plates are used to reduce friction, for example. in precision scales under a rocker or for hanging cups, etc.

The most beautiful agates come from Uruguay, Brazil, India, Arabia, Sicily; in addition, agate is also found in Bohemia, Saxony, Hesse, Hungary, Siebenbürgen and especially near Oberstein in the Nae valley. Agate processing is concentrated in the towns of Oberstein and Idar (Principality of Birkenfeld), which supply almost half of the world with agate products. Previously, local agates were processed here, but recently they have found it more profitable to deliver them from Brazil or Uruguay. In the named towns there are up to 200 factories, each with 4 or 5 grinding stones driven by water mills; up to a million marks worth of raw agate is delivered here annually to various grinders; in a word, it is one of the most interesting industries in Germany. The art of artificially coloring agates is also especially developed here, as was done in ancient times, taking advantage of the porosity of chalcedony, which is part of the agate. To artificially color agates, they are first soaked in honey water for several weeks and then the absorbed honey particles are charred by boiling with sulfuric acid; This way you get beautiful black or brown spots and stripes. The blue color of agates is caused by treatment with red cyanide salt and boiling with iron sulfate.

The oldest ornamental

The oldest ornamental stone, agate, got its name from the small river Agates in Sicily. A multi-colored, thin-layered gem with a perpendicular arrangement of fibers is called agate. In ordinary agate, translucent gray-blue layers alternate with
white translucent or almost opaque layers. In other words, agate is a translucent chalcedony with a distinct striped or patterned texture.

Agates found use back in ancient Rome, whose inhabitants knew how to tint stones with inexpressive colors. In Pliny the Elder, in the 37th book of “Natural History”, we read about this: “They (agates) are boiled. in honey continuously for seven days
and seven nights after everything earthy, all flaws are removed: a clean block with a clear blow is processed by the hand of a skilled artist, following in his work the direction of the veins and spots of the stone, cutting out of it a thing worthy of sale.”

The structure of agate is distinguished by a beautiful alternation of ribbon-shaped gracefully colored stripes – white, gray, yellow, blue and black. There are stones with such a bizarrely patterned structure that one gets the impression of moving clouds, happy, sad, or
thoughtful eyes, moss growths, ruined ruins, emerging greenery, crumbling leaves and various other things that are difficult not only to explain, but even to imagine.

G.M. Permitin wrote in 1958: “I saw a rich Uriankhai ruler with blood-colored carnelian threads with opal shades, an onyx snuff box and a stone bottle so finely carved that it floated on the water.” Here is “carnelian with opal shades”
nothing more than agate.

The art of processing precious stones has been passed down by people from generation to generation. The Greeks and Romans achieved high perfection in the processing of agates in the so-called relief-chip engraving, where the stone was given a flat oval shape in the form of
e medallion, on the front side of which heads or entire figures were carved.

With great skill, ancient masters used the layered structure of agate in the art of glyptics, where the white layer is used for the face, black and brown for hair and clothing.

In the East Gabi aimag, not far from the Daln-Turur resort, there is a deposit of Ikhjargalan agate, which literally means great happiness. This large surface placer is literally dotted with bright agate almonds sparkling in the sun. Ikhjargalan agate is incredibly diverse. Here you can find onyxes of rare beauty with a combination of white and brown stripes, which are called sardonyx; are found with a neighborhood of white and bright red lines called carneolonyx; are found with interlacing honey-yellow and white stripes – non-rachytic onyxes, and, finally, with rows of black and white lines, called Arabic onyxes.

Red, yellow and green-moss agates interspersed with tree-like inclusions of chlorite and yellow clots of iron oxides were discovered.

Mossy agates are beautiful to view, revealing dense thickets of algae or mosses in the hazy depths of the crystal. The mysterious plants in them are created by branching crystalline dendrites of green lorite. Thin streams of iron and manganese oxides create quaint cities with bell towers and bridges, ancient castles and the remains of fortresses inside the ruined agate; and golden mica flakes seem to fill the gem with a festive shimmer.

In the area of ​​the Dalan-Turu resort in Mongolia, along with blue chalcedony, colored agates with alternating bluish-blue and white stripes were discovered, the central parts of which were painted in a beautiful amber-yellow color, contrasting well with the main color.
m background.

Large localities of ornamental agate are located in the Ijevan region of Armenia, where in a thick volcanogenic sequence black layers of dense andensitic lavas alternate with tuff, more porous layers. Chalcedony and agate stones are still found in Kobuleti (Georgia) and in the Kara-Data region in Crimea.

A special variety of agate, the so-called overflow, was discovered in the Urals, where layers of chalcedony seem to flow in stripes and streams, and the color shimmers from white to blue, yellow, orange and red. But the shaitan overflow has gained wide popularity here.
t, in which a riot of colors is mixed in such a whirlwind that it resembles a riotous Satanic dance of flowers.

And one of the varieties of agate is even called aventurine for the deceptive resemblance of the stone to gold-bearing sandstone.

Although the artificial gem with picturesque sparkles, similar to glass and containing copper crystals, occurred by chance and translated from Italian means “chance”. It is believed that it was accidentally obtained at a glass factory in Murano, near Venice, when a quantity of fine copper filings fell into a vessel containing molten glass.

One of the treasures of the London Geological Museum is a huge aventurine vase with a sulfur porphyry stand. Russian Emperor Nicholas I presented it to Sir Murchison, the director of the geological survey, who bequeathed it to the museum.

Another variety acquired the name “hair of Venus” because the black and golden threads of its colors, like the rays of the sun, pierce the sparkling fiery jets of an absolutely transparent crystal. Once upon a time, hair agate was in great fashion – signets, brooches, hairpins, bracelets and other jewelry were made from it.

And in Ancient China, an amulet made of brown agate in the shape of a cicada was placed on the tongue of the deceased: this amulet, according to Chinese legends, was capable of not only resurrecting the deceased, but also making him speak (chirp) like a cicada. In the early Middle Ages, it was believed that wearing agate as an amulet or jewelry made a person pleasant in society, and his conversations more meaningful and expressive.

In different eras and among different peoples, agate was considered a talisman that saved from poisons, including snake poisons. It was credited with the ability to quench thirst and sharpen vision, patronize the owner, give him strength and eloquence, and turn away everyday storms and hurricanes from him.

There is a legend that when Satan was cast into hell, he dropped an agate from his crown, which turned into a cup. Joseph of Arithea allegedly collected the blood of Jesus Christ drop by drop into this cup and therefore became the founder of the Order of the Holy Grail. This cup, according to this legend, was a large agate cup from the treasures of the Vienna Hofburg. And products made from agate have been known since ancient times: for example, agate beads dating back to the fifth century BC were discovered in the tombs of Alushta. To be more precise, at the dawn of its history, agate stones were the first materials from which man made seals and carved jewelry (gems).

Stones with a carved pattern – intaglios – were used by the ancients mainly as seals, and stones with a convex image – cameos – were used as decorations thirty centuries BC (during the so-called Aenean culture).

The largest agate product is an almost flat dish, 75 cm in diameter, carved from a single stone, kept in the Art History Museum in Vienna.