Carnelian is a type of silica mineral quartz that is found to be translucent to opaque. This Chalcedony variety is found in medium shades of yellow, orange, and red. In the market, you may find these gems having a pattern of all three hues or one, solid color. Within all the different types of carnelian, the variety having a reddish-orange hue is considered to be the most valuable. On the Mohs Scale of Mineral Hardness, carnelian ranks an impressive seven, making them tougher than knives and nails.