Rounded botryoidal purple crystallized quartz in a cluster without matrix.
Mamuju, located on the western coast of Sulawesi Island in Indonesia, is the primary source of the material widely marketed under the trade name grape agate. Geologically, the deposits are situated within volcanic and hydrothermal environments, where silica-rich fluids filled cavities and gas bubbles in ancient lava flows, precipitating mineral layers within altered clay pockets. Mineralogically, despite its popular moniker, the material is not a true banded agate; rather, it consists of spherical, botryoidal clusters of tiny microcrystalline quartz crystals (often purple amethyst or soft green varieties colored by trace inclusions). Historically, mining in the remote, rugged terrain around Mamuju began around 2014, and the distinctive spherical specimens burst onto the international mineral market around 2016, quickly becoming a global favorite among collectors.
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