chalcedony

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic. Chalcedony's standard chemical structure (based on the chemical structure of quartz) is SiO2 (silicon dioxide).

Chalcedony has a waxy luster, and can be semitransparent or translucent. It can assume a huge variety of colors, however the ones maximum generally seen are white to gray, grayish-blue or a shade of brown ranging from pale to almost black. The color of chalcedony bought commercially is frequently enhanced by means of dyeing or heating.

The name chalcedony comes from the Latin chalcedonius (alternatively spelled calchedonius). The name appears in Pliny the Elder's Naturalis Historia as a term for a translucid kind of Jaspis. The name is probably derived from the town Chalcedon in Asia Minor.. It is a hapax legomenon (the term for a word found nowhere else) so it is hard to tell whether the precious gem mentioned in the Bible is the same mineral known by this name today.

History

Fine examples of first century objects made from chalcedony, possibly Kushan, were found in recent years at Tillya-tepe in north-western Afghanistan. Hot wax would not stick to it so it was often used to make seal impressions. The term chalcedony is derived from the name of the ancient Greek town Chalkedon in Asia Minor, in modern English usually spelled Chalcedon, today the Kadıköy district of Istanbul.

In the 19th century Idar-Oberstein, Germany became the world's largest chalcedony processing centre, in particular agates. Most of these agates were from Latin America, in particular Brazil. Originally the agate carving industry around Idar and Oberstein was driven by local deposits that were mined in the 15th century. Several factors contributed to the re-emergence of Idar-Oberstein as agate centre of the world: ships brought agate nodules back as ballast, thus providing extremely cheap transport. Also, cheap labour and a superior knowledge of chemistry allowing them to dye the agates in any colour with processes that were kept secret helped. Each mill in Idar Oberstein had four or five grindstones. These were of red sandstone, obtained from Zweibrücken; and two men ordinarily worked together at the same stone.

Geochemistry

Structure

Chalcedony was once thought to be a fibrous variety of cryptocrystalline quartz. More recently however, it has been shown to also contain a monoclinic polymorph of quartz, known as moganite. The fraction, by mass, of moganite within a typical chalcedony sample may vary from less than 5% to over 20%. The existence of moganite was once regarded as dubious, but it is now officially recognised by the International Mineralogical Association.

Solubility

Chalcedony is more soluble than quartz under low-temperature conditions, regardless of the two minerals being chemically equal. This is concept to be due to the fact chalcedony is extraordinarily finely grained (cryptocrystalline), and so has a completely excessive surface place to quantity ratio. It has additionally been suggested that the higher solubility is because of the moganite thing.

Solubility of quartz and chalcedony in pure water

This table gives equilibrium concentrations of total dissolved silicon as calculated by using PHREEQC (PH Redox Equilibrium (in C language, USGS)) the usage of the llnl.Dat database

Blue Chalcedony is an extraordinary crystal for public speakers and those who talk for a living. Lawyers and political audio system may advantage from touching this stone to the end in their tongue at the same time as taking note of their opponents to enhance their counter arguments.

Actors may rub it in opposition to their lips and throat, at the same time as singers can also drink a pitcher of water in which Chalcedony has soaked for an hour before going on stage. Wearing this crystal around the neck allows triumph over level fright and the worry of public speakme.

As a stone of peace and peace-making, Blue Chalcedony encourages stillness and calm in the domestic for the ones at odds with each other, vying for their region in the pecking order. It is likewise useful for each day journeys to paintings, or traumatic journeys concerning youngsters.

Chemical FormulaSiO2
ColourWhite, Blue, Red, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black, Banded, Multicoloured
Hardness6.5 - 7
Crystal SystemHexagonal
Refractive Index1.54 - 1.55
SG2.63 - 2.65
TransparencyTranslucent to opaque
Double Refraction.009
LusterVitreous to waxy
CleavageNone
Mineral ClassQuartz (Chalcedony)

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