The words carnelian and sard are often used interchangeably, but they can also be used to describe distinct subvarieties. The purported differences are as follows:
|Colour||Lighter, with shades ranging from orange to reddish-brown.||Darker, with shades ranging from a deep reddish-brown to almost black.|
|Hardness||Softer||Harder and tougher.|
|Fracture||Uneven, splintery and conchoidal||Like carnelian, but duller and more hackley.|
It should be noted that all of these properties vary across a continuum, and so the boundary between carnelian and sard is inevitably blurred.
Carnelian was used widely during Roman times 2,000 years before the present era to make signet or seal rings for imprinting a seal with wax on correspondence or other important documents. Hot wax does not stick to Carnelian.
The word carnelian is derived from the Latin word caro, carnis meaning flesh, in reference to the flesh color sometimes exhibited.