other names: /
mineral class: Oxides and hydroxides
chemical formula: SiO2
Chemical elements: Silicon, oxygen
Similar minerals: Chalcedony
crystal structure: trigonal
mass density: 2,6
magnetism: not magnetic
Mohs hardness: 7
stroke color: White
General information about Onyx:
onyx refers to one of the quartz counted mineral, which represents within this group a variety of fibrous chalcedony. Thus, the onyx is a representative of the oxides. The name onyx has been in use in German-speaking countries since the Middle Ages and comes from Latin, where "ungius" meant claw or fingernail. Incidentally, the word onyx is also often used to refer to onyx marble, a limestone and sintered rock of green, brown or yellow color.
Natural onyx usually appears deep black and has a white band that gives it the appearance of dark marble. Even chalcedones, which are pure black, are called onyx. The brown-white sard-onyx and the red-white carnelian are colored varieties.
The onyx forms microscopically fine, homogeneous appearing crystal fibers in dense tubers or masses. Despite the mostly deep black appearance, the line color of the mineral is white. The onyx is of glassy gloss, the transparency ranges from transparent to completely opaque. With a Mohs hardness of 7, the onyx is one of the harder minerals. His break is musselig like all quartz. With the exception of hydrofluoric acid, onyx is not soluble in any acid.
Origin and occurrence:
Onyx forms as a primary mineral from solutions with a high content of silicates. By admixtures of the elements iron and manganese creates the dark color. Naturally formed onyx is rarely found. The deposits are sparse and are scattered among isolated regions of certain countries. These include Brazil, Mexico, Madagascar, the USA, India and Pakistan. In Germany, there are significant localities in Baden-Baden, Calau and Saalhausen.
Use by humans:
The onyx has been in demand as a gemstone since the Middle Ages. Because of its deep black color jewels made from the mineral were often worn for mourning occasions. Above all, elaborate rings and brooches as well as cufflinks are still often made from onyx. Also carved gems as jewelry ornaments for necklaces, brooches and as small picture motifs were treasured in the past.
Because of its distinctive appearance, the onyx is sought after today as a gemstone, the rare natural minerals can barely meet the need. Therefore, many fakes are on the market that can be made in different ways. Due to its porous structure, the agate is perfectly suitable for deep blackening. Often the dull polished obsidian is sold as onyx. Another possibility of counterfeiting is the treatment of gray chalcedony with acid, which darkens their color. A distinction between genuine and forged copies is usually possible only by a mineralogical analysis.