Carnelian, also spelled “Cornelian” is a specific type of Microcrystaline Quartz called Chalcedony. It contains micro crystals that have been tinted or coloured by trace elemental iron (ferrous nitrate) and then formed into a fibrous aggregate body. The colour ranges from an opaque reddish brown to a translucent reddish orange colour that resembles fine Burmese Red Jade. Most Carnelian is varied in tone, hue and saturation. That is, when you view it by looking through it towards a strong light, you can observe banding or clumping of colours. The finest is uniformly coloured regardless of how you view it.
The best Carnelian comes from the Southern Hemisphere, specifically India. Good commercial qualities come from South American locales in Uruguay and Brazil. It is a tough and hardy stone, suitable for every day wear and yet, finer qualities are at home anywhere and for the finest occasions.
Modestly priced, it is in the same general neighborhood as Garnet or Amethyst, and is at home in Silver or Gold, with or without Diamond accents. As you can see from the picture, it is also a good carving medium, hence the confusion with fine Jade.