Chalcedony Gemstones - Many different gemstones
Introduction
This is a form of silica that is cryptocrystalline in nature and has minute growths of Morganite intertwined with the mineral quartz. Although these are two types of silica minerals, they are different in structure. Quartz has a Trigonal crystals structure while Morganite has a monoclinic one. Chalcedony is chemically known as silicon dioxide, and this is the natural chemical stricture of all quartz minerals.
Chalcedony, is a gemstone that has a waxy luster and has a transparency that is translucent or semitransparent. This is a gemstone that comes in many colors but is commonly found in white to gray, or grayish blue. It also can be found in shades of brown, that can be said to be pale, and sometimes gets so dark, that it can only be said to be black.
The name chalcedony was derived from the Latin name of Chalcedonius, which is sometimes spelled as Clachedonius. This is a name that is mentioned in the book written by Pliny the Elder, known as Naturalis Historis, or the Natural History of the World, and it is used as a term for the translucent variant of Japsis. The name is sometimes believed to have been derived from the town of Chalcedon, which is found in Asia Minor. In the Book of Revelation, the name Khalkedon, appears; this is a Greek word which is not heard of anywhere else, and is thus known as a Hapax Legomenon. The name therefore makes it very hard to tell whether the mineral that was named in the Bible is the same one that is toady known as Chalcedony.
The chemical nature of chalcedony
This is a silicon dioxide mineral and is a quartz. It has various colors and has both a monoclinic or Trigonal crystal system and it does not have any cleavage. It is quite a hard stone with a hardness of 6 to 7 on the Mohs scale. It has an uneven fracture, which is also termed as conchoidal. It also has a waxy, dull, greasy or vitreous luster. The gemstone also has white streaks and is translucent in nature. It has a specific gravity of 2.59 to 2.61.
The many varieties of chalcedony
Chalcedony has a lot of varieties, and in fact, some of the semi-precious gemstones in the world actually belong to this group of gemstones. Some of the most notable of chalcedony gemstones are:
Agate · This is one type of chalcedony, whose main character is that it exhibits and transparent but colorful patter; the stone has multicolored banding that can either be straight of curved. It is also possible to find opaque variants of agate but these are sometimes mistaken to be Jasper. One of the agate stones that has an iridescent nature and a brown background is known as the Fire Agate. There is another Agate stone which has an exceptional iridescence when pinpointed light is shone through the translucent stone, and it is known as the Iris Agate due to the special feature that resembles the iris of an eye. Landscape Agate is another special gemstone in this variety, which shows features that look like landscapes due to the presence of a wide number of different mineral impurities spread within the crystal.
Aventurine · This is another special type of chalcedony quartz stone that has great translucency and the several platy mineral inclusions found within the crystals produce a special shimmering appears, or glistening look, that is so unique that it is called aventurescence. Fuchsite, which bears a lot of chrome, is the main inclusion found in this gemstone, and it brings about a silver green or blue green sheen to the surface of the stone. It is also possible to find orange and brown varieties which are made so by the presence of trace amounts of goethite or hematite.
Carnelian · which is also spelled as Cornelian, is another form of chalcedony that has a clear to translucent transparency, and has a red to brown color. The hue of the gemstone may range from pale orange all the way to a very intense coloration that can seem to be almost black. Sard, is another gemstone in this variety that looks very much like carnelian, but it is usually brown rather than red.
Chrysoprase · this is also spelled as Chrysoprase, and is another form of chalcedony that is characterized by a green color that is brought about by the presence of nickel oxide. There is another darker form of this gemstone, and is usually called Prase; however, this is also a term that is used to describe green quartz. This means that the term Prase is usually used to describe the color of the gemstone and not really the mineralogy.
Heliotrope · this is a form of chalcedony that is also known as bloodstone. It has a high number of red inclusions brought about by iron oxide. The inclusions are oddly shaped like drops of blood, and this is why it was given the name bloodstone. It is also possible to find the stone having yellow inclusions rather than red ones, and this makes the stone to be known as Plasma.
Moss Agate · this is a form of chalcedony that is also known as Tree Agate, and is characterized by the presence of green filament-shaped inclusions, which make the gemstone to look like it has moss within it, or blue cheese. Tree Agate is also similar to moss agate, but it has a solid white appearance with green filaments, and the moss agate has a transparent background. This means that the moss seems to be suspended within the stone. This is one of the agate stones that does not have the characteristic banding, and many people claim that it should not be included in the agate group of gemstones.
Mtorolite · this is a less-known form of chalcedony, which has a green color attributed to chromium; it also goes by the name of Chrome Chalcedony. This is a gemstone that is principally found in Zimbabwe.
Onyx · this is a variant of agate that has white and black banding. The varieties of chalcedony that have red, orange, or brown colors banded with white are called Sardonyx.
A short history of Chalcedony
In the Mediterranean region, chalcedony was being used from as early as the Bronze Age. There have been archeological finds, in the Minoan Crete Island, at a place known as Knossos, where chalcedony seals, which date as far back to about 1800 BC have been found. It is the people who lived along the trade routes of Central Asia who used these chalcedony stones, including carnelian, to carve out ring bezels and intaglios. Ring bezels are the upper faceted part of a gemstone, which is projecting from the setting of a ring. Other items made of this mineral include the beads that were so popular in the Greco-Roman period.
Items have been found that come from the First Century AD, that were made from chalcedony, perhaps Kushan, which were found in recent years, in North-western Afghanistan, at a place known as Tillya-tepe. Hot wax does not stick to this gemstone and that is why it was used to make seals for high level documents. Many say that the name chalcedony was derived from the ancient Greek town of Chalkedon, which was in Asia Minor. Today the city is called Chalcedon, which is now the Kadikoy district in Istanbul.
There were three types of chalcedony that could be used in the Breastplate of the Jewish High Priest. You could see this breastplate being worn by Aaron, the brother of Moses, on which the twelve tribes if Israel were inscribed using different gemstones. The plate would have Chrysoprase, jasper and sardonyx, and there has been a lot of controversy over whether agates were used.
It was in the 19th Century, that a German region known as Idar-Oberstein became the largest chalcedony processing center in the whole world, and it specialized in processing agates. The agates used at this time came from Latin America and the main place was Brazil. At first, the agate processing industry that grew up around Oberstein and Idar, used to use Chalcedony that came from local deposits, which were mined from as early as the 15th Century.
There were several factors that led to the revival of the Idar-Oberstein processing center, making it the largest in the world once again. There were ships that carried agate nodules to be used as ballast, and this provided a cheap method of transporting the gemstones. There was also cheap and available labor, and they had advanced knowledge of how to dye the agates and give them many colors; the process of dyeing the stones was a top kept secret within the industry and only this center could bring these stones to the market. There were four to five grinding stones in each of the mills at Idar Oberstein. The grind stones were made of red sandstone, which was specially brought from Zweibrucken. Each stone was worked by two men at a time.
The Geochemistry of Chalcedony
Structure, Chalcedony was thought, at one time, to be a fibrous variety of cryptocrystalline quartz. However, more recently, it has been found that this is a polymorph of quartz that is monoclinic in nature, which is known as Morganite. The percentage of Morganite that is found within a sample of chalcedony can vary from more than 20 percent to as low as below 5 percent. There was once a lot of doubt as to whether there was any Morganite found in chalcedony; the International Mineralogical Association now recognizes the fact that Morganite is found in chalcedony.
Solubility, Under low temperature conditions, chalcedony is more soluble than other types of quartz, although the two minerals are very similar in their chemistry. The reason behind this feature is the fact that chalcedony has a very fine grain structure, which is also known as cryptocrystalline structure, and this increases the surface to volume ratio, and this makes it more soluble. Others say that the high solubility may be due to the presence of the Morganite in the crystals.
A profile of chalcedony gemstones
Chalcedony has been known to give a magical and mystical appearance that seems to glow through its silky luster. It is said that chalcedony was one of the earliest materials that was known to man for the making of tools and other items. This is a gemstone that has been named as one of those one the breastplate of Aaron. It is also said to have been used to make the foundation of the city walls that surrounded the city of the New Jerusalem.
In Mesopotamia, around 7th Century BC, Chalcedony was used in the making of official seals for royalty and other important people. However, over time, they began to see the value of the gemstone as part of jewelry and important carvings. This is a mineral that has been used to make expensive knife handles and other tools. This is a gemstone that was extensively used in the creation of cameos. It is also the stone that was used in the art of Commesso. This is a technique used in making pictures that have a very this, pieces of bright gemstones that have been cut into the required shapes. This type of art was very popular around the 16th Century in Italy, especially around Florence which was a very popular city during the Renaissance.
In some countries, one can use the terms chalcedony and agate to describe the same gemstones; in fact it can be used to describe all forms of quartz that have a crypto or microcrystalline structure. The terms cannot be used to describe stones that have macrocrystalline, large and single crystal structures as is seen in Amethyst, Citrine and Smokey Quartz; these are simply called crystalline gemstones.
The name chalcedony is used to describe a species of gemstone and not a single one. The many colors of chalcedony have their own distinct names, such as Chrysoprase, Lace Agate, and Carnelian amongst many others. However, there are those varieties that do not have a unique name and use the color as a prefix, examples are Blue chalcedony, which refers to the grey blue variety of chalcedony; Pink Chalcedony, which is the lighter and milky variety of chalcedony that has a light color reserved for rose quartz, and is milkier than the vibrant pink sapphire; and the Green chalcedony, which has a very light pastel color.
This is a gemstone that has a waxy luster, and has a translucent to opaque transparency; this is also a gemstone that drives out dread, melancholy, mental illness and hysterical behavior. It also reduces fever and prevent depression. It is believed that wearing this gemstone will help promote harmony and tranquility, and also helps one in the creative process. Apart from Brazil, the gemstone can also be found in Sri Lanka and Madagascar, and occurs mainly in sedimentary and volcanic rocks.
In summary
The name chalcedony is used by gemologists to describe all gemstones and minerals that can be said to be cryptocrystalline quartz. The most common variants are Chrysoprase, bloodstone, jasper, moss agate, onyx, agate, carnelian and petrified wood. All other forms of quartz that do not have this microcrystalline nature, such as Citrine, Rock Crystal, Smoky Quarts and Amethyst are said not to belong to the group even if the name is still used to describe them generically.
Chalcedony is also used to describe any of the cryptocrystalline quartz stones that have a blue gray hue or lavender color. These are the colors that are said to be the true colors of chalcedony. Lavender is said to be the "Actual Chalcedony" or "Chalcedony in the narrow sense". These are terms that can easily confuse a buyer who is not familiar with the naming of gemstones, and this is why other forms of chalcedony must have their own unique names; such as bloodstone, carnelian or agate.
It was originally though that this gemstone was a fibrous quartz with a cryptocrystalline nature but there has been evidence that it contains Morganite, a polymorphic quartz. Quartz has a Trigonal crystal structure while Morganite has a monoclinic one. Macrocrystalline crystals can easily be seen, but the cryptocrystalline crystals cannot be seen even under a microscope.
Chalcedony is usually quite hard, and has a value of 7 on the Mohs scale and it does not have any cleavage. This makes it ideal for any type of jewelry. Although these gemstones are found in various colors, the reddish orange variety, known as carnelian; the Chrysoprase, which has a, apple green color; the actual chalcedony, which has a lavender color; the onyx, which is black; and the deep green, which has red inclusions, also known as heliotrope or bloodstone are the most popular.
The colors of chalcedony are not always solid in nature. The bloodstone has a deep green color that has red spots. The chalcedony that has bands in known as agate. Jasper has a large variety of colors, spots or flame-like inclusions. The stones that have inclusions that look like landscape are the most valued.
