Blue Chalcedony (3) Raw Minerals Stones Rocks Collecting

Description

Origin : China

Blue Chalcedony 41-60 gr - cm 4-4.5 Raw Minerals Stones Rocks for Collection.

Chalcedony is the generic name given to quartz when it occurs in compact masses of microcrystalline silica with a fibrous-oriented texture. The name derives from the Greek Χαλκηδών (Chalkedón), referring to Chalcedon, an ancient mining town of Bithynia (today Kadiköy, in Turkey) in whose surroundings the material used to create ornaments was extracted. All varieties are considered semi-precious stones and used for ornamental purposes, since ancient times, especially for the creation of cameos and carvings.
Chalcedony is generally presented in the form of crusts or concretionary masses, of uniform color or zoned with colored streaks of various shades. Roundish (mammellonary or botroidal) and nodular aggregates are frequent.
Chalcedony is semitransparent when cut thin, opaque and with the typical ceroid luster in more massive specimens. It has a hardness of 6.5-7, slightly lower than quartz, and a granular conchoidal fracture.
The color - very variable - depends on the impurities present in the crystal lattice. Since ancient times, the color has also been modified by exposure to sunlight, heating, or contact with liquids (the stone is highly porous and allows selective absorption of liquids). Depending on the color and appearance, chalcedony takes various names.
The blue chalcedony has an ashy blue, lilac blue or bright violet blue color, the latter is the most prized variety, but also the samples from Africa are no less.
The common formation environment is the low-temperature phylonian-hydrothermal environment (for example in the internal cavity of the geodes) and metamorphic. A secondary genesis, due to the hardness of quartz, is that in detrital sedimentary rocks.