Agate forms in cavities within volcanic and sedimentary rocks through the slow precipitation of silica-rich groundwater over millions of years. This variety of quartz displays characteristic banding created by successive layers of mineral deposition, with each band representing a distinct phase of formation.
Agate's colour variations result from trace mineral inclusions—iron oxides produce reds and yellows, manganese creates purples and pinks, while chromium generates greens. The distinctive banded patterns form as silica gel fills rock cavities from the outside inward, creating the layered structure.
Agate has been utilised since the Neolithic period, with significant historical deposits in the Nahe River valley of Germany giving the mineral its name. The stone's durability stems from its 6.5-7 Mohs hardness rating and fine-grained structure, allowing for detailed carving and high polish retention.
