Carnelian

Carnelian is one of the oldest gem materials used in engraved seals and beadwork, valued since antiquity for a warm orange-to-red color that takes a fine polish and, being chalcedony, is tough enough to survive millennia of use and burial intact. Egyptian, Mesopotamian, and Roman jewelry all made heavy use of it, and much of what museums display as ancient carnelian owes its saturated color to deliberate heat treatment performed by the original craftspeople — a practice that continues, essentially unchanged, in the modern trade.

Species and variety. Carnelian is a variety of chalcedony, the cryptocrystalline form of quartz, colored by iron oxide impurities distributed through the silica. It sits alongside sard (a darker, more brownish-red chalcedony colored the same way), agate (banded), and onyx (straight black-and-white bands) as one of several color- and pattern-based names applied to the same underlying material.

Appearance and color range. Natural carnelian ranges from a pale, translucent orange to a deep, saturated red, with the most prized material showing an even, glowing color without visible banding or cloudiness. Much commercial carnelian is heat-treated — often starting from a duller, grayer chalcedony or agate — to intensify or produce the orange-red color, a treatment so old and so standard that it is not generally disclosed as a special enhancement the way it would be for, say, heated sapphire.

Hardness and everyday care. At roughly 6.5–7 on the Mohs scale, carnelian is a practical everyday stone for rings, bracelets, and carved pieces, resisting scratches from normal wear. It should still be kept away from harder gems in storage and cleaned with mild soap and water rather than ultrasonic cleaning, which can stress internal fractures common in chalcedony.

Where it is found. India has long been a major source and processing center for carnelian, with additional material from Brazil, Uruguay, and Madagascar.

Birthstone role. Carnelian is a July birthstone in the UK 2013 system, listed alongside ruby, and it appears in the historical (pre-20th-century) list for August alongside sardonyx, moonstone, and topaz — but the US 1912 and US current systems give July to ruby alone, with no carnelian. It is also the traditional tropical-zodiac stone for Virgo, which begins in August; that assignment traces directly back to the historical August entry, one of eleven signs on this site where the tropical zodiac stone is simply the old monthly stone for the sign’s starting month.