The recent discovery of colorful bamboo shaped agate casts buried in volcanic pyroclastic debris with other fossilized forest remnants is a secret Indonesian forestry officials don't want to get out. Densely populated Java has very few pristine forested areas left.
This location in Central Java lies in the midst of 11 modern day composite volcanoes,
Figure #1 - Central Java Volcanoes
including, the well know Mt Merapi often seen spewing ash by air travelers in transit from Jakarta to Bali.
Photo #1 - Mount Merapi Central Java
The basal mass of fossil bamboo is represented by well cemented, massive parallel agate tubes. I gather these were are at ground level when a deluge of volcanic ash buried the forest and left the upper portions of the plant in a confused entanglement of tapered pencil-like agate rods.
Photo #2 - Heart of Agatized Bamboo
Photo #3 - Basal Clusters of Fossilized Bamboo
There has been no scientific study of this material by paleobotanists, but as a geoscientist, I conclude that the association with other preserved forest remnants as petrified woods and leaf casts in fine ash suggest the likelihood of organic origins. The sometimes curved and mostly hollow tubes of layered botryoidal agate range from 1cm to 3cm in diameter. The hollows are at their greatest diameter at the base and taper to the tip.
Grooves and striations on the inner walls suggest a fibrous bamboo-like plant was replaced with agate. In some pieces that petrified material is still present in the core, suggesting only partial replacement.
Photo #4 - Grooved Inner Wall of Fossil Bamboo
Photo #5 - Curved Fossil Bamboo
Multiple layers with an assortment of colors indicate the chemistry of depositional solutions varied as the silica deposited layer upon layer. Intergrowths of manganese dendrites are also observed.
Photo #6 - Colorful Inner Layers of Fossil Bamboo
Preservation of this unique material appears to have resulted from burial by a volcanic eruption of siliceous volcanic ash. The decomposing volcanic ash, combined with water and oxygen over time produced acidic fluids super saturated in dissolved silica, iron and other elements along with very fine grained suspended components of volcanic debris.
Periodic rains allowed oxygen-rich surface waters to percolate down into the volcanic pile, diluting the acid chemistry and causing deposition of the silica and its suspended components using the remnant bamboo as a nucleus. Over time, repeated episodes dissolved the ash surrounding the bamboo and deposited layer upon layer of agate around the bamboo in a botryoidal form creating a surface like a cluster of grapes.
Colors of rich orange, red and purples resulted from the iron, manganese and other elements in the mix.
Photo #7 - Home of Fossil Bamboo
Locals prod the soil with long steel rods in search of hard buried treasure. The fossils lie buried in a giant slump block which scattered debris down a steep slope, which top to bottom comprises a 2 hour hike!
Typically the specimens have broken ends, as they have tumbled down a rugged slope. The diggers take their discoveries home and bury them in soil again claiming the shafts re-grow and the broken ends will be renewed.
Photo #8 - Shafts of Fossil Bamboo
Why the larger diameter bamboo has not been preserved is not understood. It may be related to the moisture content of the younger shoots at the time of burial which led to their preservation or their proximity to the soil and water table. It may just have been that this was a species of small diameter bamboo.
Photo #8 - Guardians of the Fossil Bamboo"
After a lot of hiking and exploration, the best pocket specimen of "fossil bamboo" was found back in the village. With the entire village turning out to witness the event, it took countless kretek cigarettes and a fist full of Indonesian Rupiah to consummate a deal and secure our prize.
Photo #10 - Negotiating for a Fossil Bamboo Specimen"
Photo #11 - Custom Beads Cut By Gary Andruss
