Carnelian / Sard
Polished carnelian/sard pebbles. Scale is in millimeters.
General Category Chalcedony variety Chemical formula Silica (silicon dioxide, SiO2) Identification Molar mass 60 g / mol Color Brownish-red Crystal system Trigonal Cleavage Absent Fracture Uneven, splintery, conchoidal Mohs scale hardness 6 - 7 Luster Vitreous, dull, greasy, silky Streak White Diaphaneity Translucent Specific gravity 2.59 - 2.61 References 
Carnelian (also spelled cornelian) is a brownish-red mineral which is commonly used as a semi-precious gemstone. Similar to carnelian is sard, which is generally harder and darker. (The difference is not rigidly defined, and the two names are often used interchangeably.) Both carnelian and sard are varieties of the silica mineral chalcedony colored by impurities of iron oxide. The color can vary greatly, ranging from pale orange to an intense almost-black coloration.
The bow drill was used to drill holes into carnelian in Mehrgarh between 4th-5th millennium BC. Carnelian was recovered from Bronze Age Minoan layers at Knossos on Crete in a form that demonstrated its use in decorative arts; this use dates to approximately 1800 BC. Carnelian was used widely during Roman times to make engraved gems for signet or seal rings for imprinting a seal with wax on correspondence or other important documents. Hot wax does not stick to carnelian. Sard was used for Assyrian cylinder seals, Egyptian and Phoenician scarabs, and early Greek and Etruscan gems. The Hebrew odem (translated sardius), the first stone in the High Priest's breastplate, was a red stone, probably sard but perhaps red jasper.
The word carnelian is derived from the Latin word caro, carnis meaning flesh, in reference to the flesh color sometimes exhibited. According to Pliny the Elder, sard derives its name from the city of Sardis in Lydia, but it more likely comes from the Persian word سرد sered, meaning yellowish-red.
Distinction between carnelian and sard
The names carnelian and sard are often used interchangeably, but they can also be used to describe distinct subvarieties. The general differences are as follows:
Carnelian Sard Color 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 hackly.
All of these properties vary across a continuum, and so the boundary between carnelian and sard is inevitably blurred.
- ^ Rudolf Duda and Lubos Rejl: Minerals of the World (Arch Cape Press, 1990)
- ^ Kulke, Hermann & Rothermund, Dietmar (2004). A History of India. Routledge. 22. ISBN 0415329205.
- ^ C. Michael Hogan, Knossos fieldnotes, Modern Antiquarian (2007)
- ^ Section 12 of the translation of Weilue - a 3rd century Chinese text by John Hill under "carnelian" and note 12.12 (17)
- ^ a b c d Chisholm, Hugh, ed (1911). "Sard". Encyclopædia Britannica (11th ed.). Cambridge University Press.
- ^ Chisholm, Hugh, ed (1911). "Carnelian". Encyclopædia Britannica (11th ed.). Cambridge University Press.
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