Agate

Agate is a banded form of chalcedony, the finely fibrous kind of quartz (silicon dioxide), and Wikipedia classes it as a variety of quartz. Its layers of differently coloured chalcedony usually run in rings that follow the shape of the hollow it grew in, though some lie in flat parallel lines. Most agates grow as nodules in the gas pockets of volcanic rock, others in veins or by replacing fossils, and no one has yet made one in a laboratory. Iron oxides give most bands their colour, and many dull agates on sale have been dyed or heated. Theophrastus and Pliny both say it was named after the River Achates in Sicily. People shaped agate into tools in the Stone Age, and into jewellery and seals from Sumerian times onward. Cunningham gives agate to Mercury and uses it for strength, courage, long life, love, healing and protection: worn while gardening for fruitful plants, as a truth amulet, and by children as a guard against falls. Hall calls it a slow-working grounding and balancing stone that brings strength, self-confidence, a love of truth and courage, and credits it with cleansing and healing effects.