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cornelian(kôr–, kər–), variety of red chalcedonychalcedony
[from Chalcedon], form of quartz the crystals of which are so minute that its crystalline structure cannot be seen except with the aid of a microscope. Chalcedony has a waxy luster and is translucent to transparent.
..... Click the link for more information. , used as a gem. It is distinguished from sard by the shade of red, carnelian being bright red and sard brownish. The red coloring is apparently caused by iron oxide.
a variety of the mineral chalcedony with a reddish yellow or red color caused by admixtures of ferric oxide. Varieties of agate consisting of alternating layers of bright red or reddish yellow and milky white coloring are called sardonyx. Carnelian and sardonyx are valuable and widespread decorative stones. They are used for making beads and as stones to be set in rings, brooches, and decorative boxes. Cut insets made of carnelian and sardonyx (cameos and gems) and small cut bottles and snuff boxes made of carnelian are highly valued.