Agate slice from Brazil (1kg) on brass stand

Agates form in volcanic cavities created by gas bubbles trapped in basaltic lava. These cavities, blocked by the viscosity of the cooling lava, were then filled by silica-rich hydrothermal solutions. Each successive infiltration brought different oxides - haematite, limonite, manganese or chlorite - giving rise to these concentric layers of varying shades.
On this slice, the dominant golden-brown hues contrast with the crystallised core, testifying to later crystallisation in the cavity.
Mounted on a brass base, this agate slice reveals even more detail when illuminated, offering a subtle interplay of transparency and contrast.