Mineral

Botryoidal Black Chalcedony Geode (Black Grape Agate)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Black to dark charcoal grey; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Habit: Botryoidal (grape-like clusters); Specific Gravity: 2.6-2.65

Hardness: 6
Color: Black to dark charcoal grey
Luster: Waxy to vitreous

Identified March 18, 2026More mineral →

Explore Botryoidal Black Chalcedony Geode (Black Grape Agate) in the encyclopedia →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater in volcanic cavities or sedimentary pockets. These often form in basaltic gas bubbles (vesicles) over millions of years. This specific specimen likely originates from Indonesian or Moroccan volcanic deposits.

Uses & applications

Primary use is for lapidary work, high-end interior decoration, and metaphysical crystal collecting. It is popular in jewelry when sliced or cabbed to show the internal banding.

Geological facts

The term 'botryoidal' comes from the Greek word 'botrys,' meaning a bunch of grapes. While clear or white chalcedony is common, the deep black coloration is caused by inclusions of minerals like manganese oxide or iron during the formation process.

Field identification & locations

Identify by its 'bubbly' or rounded surface texture and high hardness (it cannot be scratched by a steel knife). Look for the lack of visible crystal faces, which distinguishes it from black quartz or tourmaline. Commonly found in Indonesia, Brazil, and Morocco.