Metal-coated crystals are artificial products made by coating
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s, such as
quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
, with metal to give them an iridescent metallic sheen. Crystals treated this way are used as
gemstone
A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...
s and for other decorative purposes. Possible coatings include
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
,
indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts p ...
,
titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
,
niobium
Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...
and
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
. Other names for crystals treated in this way include aqua aura, angel aura, flame aura, opal aura or rainbow quartz.
Production
Such products are created in a vacuum chamber by
vapour deposition
Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.
In typical CVD, the wafer (substr ...
. Quartz is heated to 871 °C in
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
, and golden wire is heated to even higher temperature, either by resistive heating with direct electrical current, or by magnetron. Gold sublimation occurs, and subsequently deposition on crystal's surface.
When viewed under a gemological microscope in diffused direct transmitted light, aqua aura displays the following properties:
*a coppery surface iridescence in tangential illumination
*diffused dark outlines of some facet junctions
*a patchy blue colour distribution on some facets
*white facet junctions, irregular white abrasions and surface pits, where the treatment either did not "take" or had been abraded away.
The brilliant color of these products is the result of
optical interference
In physics, interference is a phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude. Constructive and destructive ...
effects produced by layers of metal.
See also
*
Rhinestone
A rhinestone, paste or diamante is a diamond simulant originally made from rock crystal but since the 19th century from crystal glass or polymers such as acrylic.
Original
Originally, rhinestones were rock crystals gathered from the river ...
References
External links
{{commonscat inline, Aqua aura
Crystals
Gemstones