‘Fossil Bamboo’

Mineral: Chalcedony (Agate), Limonite.
– Specimen Size: 7 x 6 x 6 cm (appr.)
– Found: Indonesia (Java)
Photo: Leo Jahaan

Notes: Specimens such as this are known as ‘Fossil Bamboo’ by the Javanese locals, however the material requires further research to ascertain exactly what it is and how it has formed.  A likely theory is that these hollow tubes are translucent chalcedony casts, initially formed over organic matter. Volcanic ash has probably fallen into a marsh environment, dissolving into a mineral-rich suspension which changes the chemical composition of the wetland, resulting in the growth of cryptocrystalline quartz on the surface of tough silica-rich plant or grass stems.  A likely plant candidate is Equisetum, commonly known as ‘horsetail’ or ‘puzzlegrass’, which can resemble bamboo in appearance.  Following the slow decomposition of the inner organic material, iron-rich minerals such as limonite have formed on partial surfaces and in some cases formed bog iron ‘rods’ within the now-hollow tubes.