Photo of Carnelian in Processed & Rough Form
Carnelian is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of silicon dioxide, their full chemical compound being SiO2.
Carnelian is a variety of chalcedony, which is translucent and is red to reddish-brown. It may also occur as flesh-colored chalcedony, known as cornelian or carnelian. It is slightly similar in appearance to its relation, the dark brown chalcedony, sard.
The colour of cornelian is caused by colloidally dispersed hematite. Other reddish chalcedonies may have been colored by heating since if they contain disseminated iron compounds the heating will oxidize them. Over the years, simple trade-accepted heat treatments have been invented to convert carnelian to sard, transforming dull gemstone colors into more marketable hues.
Chalcedony is a compact form of silica, composed of microscopic quartz crystals. It is softer than quartz and denser than opal. Its appearance may range from transparent to translucent to opaque.
It occurs in some fossils, such as petrified wood. It forms in cavities in rocks of different types, especially lavas, and develops at relatively low temperatures.
Visible examples would be the carnelian in Uruguay and California. Most are agates colored with ferrous nitrate solution. When held against the light, the colored variety shows stripes, while the natural variety has a cloudy distribution of color.
The best qualities of carnelian come from India (also called "cambay stone"), where the brown tints are enhanced to red by exposure to the sun. Yellow carnelian is called "canary stone."
The specific gravity [?] for Carnelian is 2.61, its refractive index [?] is 1.53-1.54, and its double refraction [?] is 0.004.
History
Carnelian (or cornelian) derives its name from the Kornel type of cherry because of its color. In antiquity it was thought to still the blood and soften anger.
Industrial Usages
India has produced most of the finest sard and cornelian since the fourth century BC but there are many other sources worldwide. Much commercial material comes from various deposits in Brazil and Uruguay. Some beaches on the east coast of England produce cornelian.
You May Also Like...
Chalcedony: Chalcedony is a compact form of silica, composed of microscopic quartz crystals. It is softer than quartz and denser than opal. Its appearance may range from transparent to translucent to opaque. The main types are chalcedony, which is uniformly colored, and agate, which has curved bands or zones of varying color. Varieties include the red to reddish brown, translucent carnelian, the red, opaqu (read full)
Sard: Sard is the uniformly colored red-brown or brownish-yellow variety of Chalcedony, which in turn is a microcrystalline variety of Quartz. There is no strict separation between sard and cornelian/carnelian (red to reddish brown), because they are both chalcedonies found in the same deposits and were employed for the same objects. The tints of a sard stone may be reddish or orange. Good-quality mat (read full)
Sardonyx: Sardonyx is a gem variety of reddish-brown colored sard with white or black banded chalcedony or onyx, used to make cameo with the raised black, red, or brown background. It is an example of a layer stone subvariety of Chalcedony, which in turn is a cryptocrystalline variety of Quartz. Layer stones are multi-layered materials used in the art of gem-carving and engraving, also called glyptography (read full)
