Agate: meaning, properties and lore

The mineral

Agate is a common semiprecious silica mineral that is a variety of chalcedony occurring in bands of varying colour and transparency. Encyclopaedia Britannica describes it as essentially quartz, so its physical properties are in general those of that mineral. Gemological work describes agates as consisting mainly of fibrous microcrystalline low-α quartz, which makes them macroscopic banded chalcedony.²

On the Mohs scale its hardness is 7. Its refractive index is 1.54 to 1.55 and its specific gravity is 2.63 to 2.65.¹²³

Agate has a vitreous lustre and is translucent. Most agates occur in cavities in eruptive rocks or ancient lavas, and their banded structure has successive layers approximately parallel to the sides of the cavity. Agate is thought to form when silica-bearing water penetrates gas bubbles in cooled lava, gels, and hardens with silica crystallizing as quartz or chert.¹²³

Most commercial agate is artificially stained so that dull gray stones become valuable for ornamental purposes. Agates from Brazil are often dyed, especially those with more intense colors. Neon-like pink, blue, or green colors in agate are always dyed.²¹

The play of colour in fire agate is caused by inclusions of goethite or limonite. Each layer is dusted with the iron hydroxide mineral goethite, which provides the brown bodycolor. Ultra-thin goethite coatings cause a colorful iridescence, primarily in red, golden orange, and green, occasionally violet to blue, through interference between light rays reflected and refracted from the ultra-thin layers.¹⁴

Agate deposits exist in Brazil, Argentina, Uruguay, Mexico, Poland, Botswana, India, Australia, and the United States, and agate is found throughout the world. In the United States it is produced in several western states, and Oregon, Washington, Idaho, and Montana are the chief sources of gemstones. Agates were historically found in the Idar-Oberstein region of Germany, and large deposits were discovered in Rio Grande do Sul, Brazil in the 1800s.¹²

History and lore

Pliny the Elder, in Natural History, Book 37, recorded that agate was once held in high esteem but by his time enjoyed none. He wrote that agate was first discovered in Sicily near the river of the same name and was later found in many countries. He also recorded that its size can be exceptional and its varieties very numerous.⁵

Pliny recorded that agates were found in Trachis, Parnassus, Lesbos, Messenia and Rhodes, and in Phrygia, Thebes and Cyprus. He wrote that agate was sometimes called sacred agate because it was thought to counteract the bites of spiders and scorpions. He also recorded that Indian agates were effective against scorpion and spider venom.⁵

Pliny recorded that the Magi claimed agate resembling a lion's skin was effective against scorpions, and that burnt in Persia its fumes averted storms and waterspouts. According to the Magi, a single-colour agate made athletes invincible.⁵

The author of the poem Lithica praised agate as a stone that helps a woman gain a man's heart and win her desire. Marbodus, Bishop of Rennes, in the eleventh century, declared that agates make wearers agreeable and persuasive and give them the favor of God. Camillo Leonardo claimed that agates give victory and strength to their owners and avert tempests and lightning.⁶

Agate wearing was believed to cure insomnia and was thought to ensure pleasant dreams. Cardano wrote that while wearing agate he had many misfortunes he could not trace to any fault of his own, so he abandoned its use, though he said it made the wearer more prudent. In another treatise Cardano stated that all varieties of agate make wearers temperate, continent, and cautious, and so are useful for acquiring riches.⁶

Psellus (eleventh century) advised agate for inflamed eyes and headaches, and said it checked menstruation and prevented dropsy water accumulation. In Persia agate was believed to ward off tempests, and the red agate idol Hobal in the Kaaba was prayed to for rain in time of drought.³

The most celebrated idol of the Kaaba at Mecca, Hobal, was a figure of a man cut from red agate, according to tradition brought from Belka in Syria. The agate-working industry grew up centuries ago in the Idar-Oberstein district of Germany, where agates were abundant. After 1900 most agates were supplied by Brazil and Uruguay.³²

The fourth amulet of a Greek lapidary, probably written in the third or fourth century, bore the druops, probably a variety of agate favored as protection against the Evil Eye. The sixth amulet used the ophiokiolus stone, most probably a banded agate, said to protect wearers from the ocean.⁶

Birthstone and other links

Practitioners say that in China agate is considered a symbol of longevity, good fortune, and protection. This is a modern practitioner link, not an ancient Chinese tradition.

Practitioners associate agate with good luck, and with promoting good health, wealth, and happiness. This is a modern practitioner link set out in present-day crystal books.

What crystal practitioners say

Practitioners of metaphysics associate agate with the mind and with work. Modern practitioners believe agate enhances communication and bridges the physical and spiritual worlds. Practitioners believe agate stimulates analytical thinking, which makes it a popular talisman for individuals in business.

Crystal practitioners treat agate as a support for courage. Believers say black agate is used as a grounding stone.

Practitioners link agate with rest and meditation. Placed under the pillow, agate was thought to encourage restful sleep and pleasant dreams. Buddhist monks believed that agate prayer beads could help purify the mind and deepen meditation.

Crystal practitioners regard agate as capable of soothing thirst when placed in the mouth.

What testing has found

Researchers at the Gemological Institute of America studied Moroccan agate from Sidi Rahal and suggested that agate crystallization was associated with the activity of Fe3+ in silica-bearing fluids, based on the moganite and Fe compound content.⁷

Fire agates of the finest quality can rival Australian black opal in appearance. Fire agate is considered more durable than opal and suitable for virtually any jewelry application.⁴