Indonesian Agatised Fossil Coral

Fossil Coral occurs throughout the world. Reefal Limestones are in essence fossil remnants of coral reefs. Massive preservation (fossilization) of coral reefs has occurred periodically over hundreds of millions of years.

The calcium is leached out of the limestone and replaced by silica. This process, referred to as silicification,
The result of the silicification of buried coraline limestone is the creation of "agatised" fossil coral. (Agate is a common term for micro or cryptocrystaline quartz or "chalcedony").

Agatised fossil corals are known to occur in many parts of the world; Thailand, China, USA, Indonesia and dozens of other countries. But it is rare that the silicification process takes place yet preserves the coral polyp image.

In Indonesia, there are several sites where the silicification process has occurred probably caused by decomposing deposits of volcanic ash periodically blanketing the countryside and near-shore marine environment. The modern day evidence are agatised cobbles and boulders of early Moicene (16-24 million year –old) coraline limestone deposits.
The fluid chemistry of elements replacing the limestone in some locations preferentially preserved the image of the coral polyps of the ancient coraline limestones.

Unfortunately, in most cases, the replacement of the calcium only took place in the outer skin of the rock and the inner cores contain a mere leached sponge-like material in which the coral polyp image has been destroyed. In other cases, the reaction fully replaced the limestone leaving a solid lump of nondescript agate.

The agatised fossil coral is collected along stream beds or by digging pits in the mountains where exposures of the Miocene limestones outcrop.

Nice jewelry quality material is only a very small fraction of the agatised fossil coral collected.

Often only a slab from the agatised top of the coral head exhibits well defined polyp images. This has received the most silica impregnation and exposure to color enhancing elements in the groundwater such as iron and manganese.
Less than 5% of the agatised rough is polishable. Of that 5%, another 70% is lost in trimming out clear defined polyp images, cutting cabochon shapes and polishing. All told, perfect images are relatively rare.

Colors vary widely and can be enhanced by heating much as with Carnelian and other agate varieties.

We ship bulk or select rough, specimens, slab rough and can cut your cabochon order.