Grape Chalcedony – Sulawesi, Indonesia – 6,5g

Grape chalcedony is a relatively new discovery in the mineral market. The first samples were found in 2016 on the Indonesian island of Sulawesi, specifically in the Manakarra area. Grape chalcedony is a variety of quartz and is characterized by characteristic spherical aggregates called spherulites, which are formed by precipitation from silica-rich (SiO₂) jelly-like solutions. These spherical structures, often up to 1 cm in size, are made up of fine filaments of the same length that are closely packed together. The individual spheres are often fused together or to the underlying rock, forming a shape resembling a grape, giving rise to their name.

Grape chalcedonies are known for their soft to intense colors, especially purple and green. The purple color is caused by the presence of manganese, while the rarer green specimens get their color from other impurities in the rock. Samples may also be covered with tiny quartz crystals, which give a shiny appearance.

They form during low-temperature hydrothermal processes in fractures and cavities in volcanic rocks. This process allows chalcedony to crystallize into typical botryoidal shapes.

Like all forms of quartz, grape chalcedony is highly resistant mechanically and chemically, making it a durable material suitable not only for collecting but also for making jewellery such as pendants or earrings.