Oxides and hydroxides: Chalcedony

Diagnostic Card.
Photo: Great blue chalcedony instance concretion of Gutenberg (the Austrian province of Carinthia).

Si O ₂
Crystal system trigonal
Hardness 7
Specific gravity 2.6
Cleavage is absent
fracture conchoidal
Colour colorless, raznookra- Weighted
Color white powder
Shine from the glass to the fat

Under chalcedony understood as the entire group of cryptocrystalline silica minerals (agate, onyx, chrysoprase, carnelian, Sarder etc.), And actually chalcedony, that is, its bluish or yellowish-gray variety. The name of chalcedony got on the ancient city in Asia Minor - Chalcedon. In contrast to the shiny as glass, quartz macrocrystalline mineral groups (such as rock crystal, amethyst, etc.), Chalcedony inherent in wax, and on how often a dull sheen.

Chalcedony is an aggregate of tiny fibrous crystals of silica, parallel to each other. They are closely intertwined with particles of amorphous silica hydrate and microcrystalline quartz grains. Microcrystals of quartz typically connected in parallel strips or spherical aggregates. When a small thickness of translucent chalcedony; in other cases it is opaque. Gloss glass; mineral is moderately hard and very durable. The term "chalcedony" in terms of the use of jewelry represent only a stone with a faint color, milk or opal color, light gray, blue-gray or pale brown. Coloration is uniformly distributed or spots of varying intensity.

Under the microscope, it is seen that chalcedony is composed of fine fibers oriented perpendicular to the surface of the discharge; macroscopically it is presented grozdevidnymi, reniform or stalaktitopodobnymi secretions, sectional - radiating. The porous structure of the mineral determines its ability to easily absorb dyes. In natural chalcedony banding with the naked eye is not observed, but the trade is sometimes called chalcedony and artificially colored in pale blue agates.

Diagnostic features.
With moderate warming or just prolonged exposure to the sun is the color of some chalcedony can vary from yellow and brown to red and orange-red.

Origin.
Chalcedony occurs in cavities or fissures in igneous or sedimentary rocks. In them it is deposited as a secondary mineral of silica-rich solutions, forming a layer or crust, or nodules or stalactites. In some cases, chalcedony formed by the substitution of other silica materials, including wood, bone, mollusk shells, corals.

Place of Birth.
Chalcedony deposits are widespread. Especially famous chalcedony Brazil, India, Madagascar and Uruguay. In ancient times, chalcedony was a favorite stone for cutting gems, believed that he protects from mental disorder and melancholia. Today, the stone used in stone-cutting art for beads, cabochons. Among the ancient Indian fields are known (in the state of Bombay) and Tuscan, which develops in the days of the Etruscans. Currently, the main varieties of chalcedony are mined in Brazil and Uruguay. Small amounts chalcedony available in Italy.

Application.
Since antiquity chalcedony was used mainly for the manufacture of intaglio, stamps, seals, cameos. Now it is mainly used for production of decorative and applied art.. cutlery, boxes, ashtrays, etc. In the jewelry business for chalcedony mainly used cabochon cut. Varieties. The most notable species banded with color - Agate (white, reddish-brown and yellow) and black and white onyx. Among the translucent varieties with uniform color, stands carnelian orange-red (carnelian) and more brownish (Sarder), chrysoprase uniformly apple-green and yellow-green. Less known heliotrope - dark green with a blood-red spots and agate, the flywheel - bright and opalescent, with inclusions of filamentous minerals, vegetable-like shape.

Varieties of chalcedony: Agate

Since ancient times people have used it for the manufacture of seals and amulets. Agate interesting color distribution in the form of a curved or concentric bands. The colors are mainly dull - gray, yellow, brown, green and less blue. The main deposits of this gem found in Brazil and Uruguay. From agate doing mostly beads and rings; of the species in which alternate stripes pinkish and whitish color, produce intaglios and cameos.

Varieties of chalcedony: Agate the flywheel (moss agate)

It is a bright and uniform, with a less pronounced zoning, but different dendritic inclusions of black and green and green, resembling moss. Moss agate is a translucent chalcedony (from a scientific point of view it is not agate!) With branching filamentous, feathery inclusions steblevidnymi and amphibole or layered silicates.

In the ground-stone of their clusters resemble moss (hence the name). If the inclusions are so many, the breed is called "moss jasper" (that is scientifically incorrect).

In nature, moss agate occurs as veinlets, performing mostly cracks in volcanic rocks; and in alluvial deposits in the form of shingles. Best Quality Mokhovikov come from India. Among other suppliers may be noted, China and the United States (Colo., Michigan, Oregon, Utah, Washington, Wyoming). Beautiful Moss Agate are also found in the CIS (the Caucasus) and in Bulgaria.

As a result, infiltration of iron oxide may appear nice red-brown color. Currently, large quantities of this mineral comes from Brazil and India. Agate the flywheel can be processed in the form of small plates, cabochons, spheres for necklaces or pendants and necklaces and brooches. Treat Moss Agate is usually in the form of thin plate-like inserts, identify their pattern, or cabochons. Applied as inserts in brooches, pendants, earrings and rings. This is a very popular stone.

Varieties of chalcedony: the dendrite-agate (dendritic, tree agate)

Dendragatom called colorless or blue-gray and milky white translucent chalcedony (from a scientific point of view it is not agate, chalcedony that is !!) with tree fern or ingrowths dendrites formed hydroxides and oxides of manganese and iron. Dendrites are usually brown or black. To the organic world, despite the external similarity with the plants ( "dendrites" - Greek-tree), they have nothing to do. Most likely they can be likened to a frost on a windowpane.

For such forms of leads fast crystallization on the walls of the finest cracks solutions, introducing manganese and iron by weathering of the host rocks. In nature, it occurs together with other varieties of chalcedony. The most famous mine-dendrite agate is Brazilian (pcs Rio Grande do Sul.); also known field in India and the United States. So as soon as the Indian-dendrite agate got to Europe through the Yemeni port of Mocha, as they are sometimes called-mocha agates.

Landscaping, or landscape, agate - it's the same dendrite-agate. but more colorful, with a relatively well-risuyuschimsya scenery, where the role of trees usually play dendrites. Often the landscape may be, and moss agate. Myukkenshteyn - Agate with "flies" - a kind of dendrite agate, in which the small dendrites did not form a uniform pattern and resemble flattened midges.

Sometimes called wood agate petrified wood, substituted silica.

Varieties of chalcedony: Agate and carnelian carnelian

The most popular uniform orange-red color; Sometimes, on the contrary, it has a variety of color shades. There are species which are not seen specific inclusions, except for the light "curtain" of liquid droplets or fracture lines. Most often fluoresces blue-white glow, which have carnelian from India is replaced by the greenish-yellow. The most important deposits are in Brazil and Uruguay. Most often used for the treatment of embedded engraving (intaglios).

Carnelian and carnelian - brownish-red and orange kind of agate and chalcedony. His name was in color, reminiscent of the color of the berries of dogwood (lat. "Kornis"), or perhaps from the Latin. "Karneus" - flesh. The most beautiful carnelian varieties come from India, from prolonged exposure to bright sunlight brownish tint disappears and is replaced by a thick orange-red tone. Most carnelian coming now on the market - it is dyed with a solution of ferric nitrate plain agate from Uruguay or Brazil. In natural carnelian color distribution of "cloud", and sanitized Agate - usually banded.

Sarder - reddish brown and yellowish variety of chalcedony, the term is being phased out. Named for the city of Sardis in Asia Minor. Artificially colored Sarder get gray chalcedony, impregnating it with a solution of burnt sugar.

Varieties of chalcedony: Chrysoprase

This is the most popular and valuable variety of chalcedony of apple-green color and the ability to gently shine through. His color he owes to the presence of tiny inclusions of nickel-containing minerals.

The color tone is not too stable, as pales when heated or prolonged exposure to the sun. To restore the color you need to hold harizopraz in a moist environment.

Chrysoprase occurs mainly from Australia, from the Urals, from California and Brazil. It is used for the production of oval plates with embedded engraving (intaglios), brooches, pendants or spheres for necklaces and bracelets. The precious and most expensive variety of chalcedony that can be framed in silver and gold.

Chrysoprase Greek name, meaning literally "golden onion", now it seems not quite clear. Under the microscope, it found radiating or sub-parallel arrangement of silica fibers. Colouring caused by adsorption and thin doped nickel compounds. Large pieces of raw chrysoprase often fractured and unevenly colored. Painting can fade in direct sunlight or by careless heating (requires accuracy soldering products). Freshen color of the stone can be, putting it at a time in a moist environment (eg, a wet cloth or the ground).

Chrysoprase deposits are confined to the Coram nickel weathering of ultramafic rocks, where it performs the cracks and form nodules. Chrysoprase is relatively rare. It used to be Ząbkowice mine in Upper Silesia (Poland), the most significant development since the XIV century. Since 1960 the best quality chrysoprase comes from Queensland, Australia. These deposits are also known in Brazil, India, South Africa, Madagascar, the CIS (the Urals, Kazakhstan) and the US (Ariz., California and Oregon).

It is used as a material for cabochons, cameos and small plastics. The best varieties of chrysoprase often handled frideritsianskoy cut: flat table is flanked on one edge of the number of small facets (cut was named in honor of the Prussian King Frederick II). In the XIX century chrysoprase also used for interior decoration (Chapel of St.. Wenceslas in Prague Sanssouci Palace in Potsdam). Chrysoprase can be confused with varistsitom, jade, prehnite, smithsonite and artificially colored chalcedony.

Hrizoprazovoy matrix called chrysoprase with white, pinkish or brown inclusions of the host rocks. They are also used in the stone-cutting business and polished as cabochons.

• Gatchell - "New Almadén snag" - arsenide and antimony sulfide (modern sulphosalts)
• Antimony - toxic metal (semi-metal) are widely used in industry, medicine and engineering
• Zirconium - a rare and non- metal and dangerous jewel in the oxide and salts
• Gold - yellow dangerous and toxic metal -date and accurate digital cable technology
• Sulphur - a golden-yellow toxic substance and a sign of volcanic activity
• Cadmium - a toxic uncirculated unknown wide range of people silvery metal
• Lead - a poisonous gray simulator silver metal and toxic metal snag
• Arsenic - poison classic medieval and modern poisoners and medicine in medicine

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Catalog minerals and gems in groups of the world

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