Grape Agate (Quartz var. Amethyst)- Mamuju Regency, West Sulawesi Province, Indonesia

Grape Agate (Quartz var. Amethyst)
Mamuju Regency, West Sulawesi Province, Indonesia
Dimensions: 3.2 x 2.3 x 2.3 cm

This is the exact specimen you will receive.

Often marketed under the trade name “Grape Agate,” this remarkable material from Mamuju, West Sulawesi, Indonesia is more accurately described mineralogically as amethystine quartz. Its distinctive grape-like spheres are composed of radially arranged quartz, creating the unusual botryoidal habit that has made this material highly sought after by collectors.

The terminology surrounding Grape Agate has been the subject of published gemological research. Laurs and Rossman (2018) examined Mamuju material and identified the grape-like aggregates as quartz rather than true agate. Subsequent Raman spectroscopy research likewise identified the material as quartz and found no detectable moganite in the samples examined, further supporting its classification as crystalline quartz rather than chalcedony (Štubňa, 2021).

The result is one of quartz's most unusual natural forms: tightly packed spheres of purple amethystine quartz that resemble a miniature cluster of grapes. Individual spheres may measure only a few millimeters across, creating a wonderfully intricate surface that rewards close inspection.

Mineralogical Note: Although “Grape Agate” remains the established trade name and the term most commonly used by collectors, amethystine quartz is a more mineralogically precise description of the purple Mamuju material examined in these studies.

References

Laurs, B. M., & Rossman, G. R. (2018). Grape-like “Manakarra” quartz from Sulawesi, Indonesia. The Journal of Gemmology, 36(2), 101–102.

Štubňa, J. (2021). Identification of “grape chalcedony” from Indonesia. Gemologický spravodajca, 1(11), 5–10.