Mohs Hardness of 7 with a trigonal crystal structure.
Sard, Onyx, as well as Sardonyx are are all varieties of Chalcedony Quartz. Carnelian is a red form of Chalcedony.
Carnelian is a chalcedony, also called Cornelian, this translucent, reddish orange variety of chalcedony was once thought to still the blood and calm the temper. It’s various shades of red are due to the presence of iron oxide.
Stones may be uniformly colored or faintly banded. It is told that the best carnelian specimens are from India, where it is placed in the sun to assist a slight change from brown shades to tints of red and orange.