Rainbow Calsilica | Man-Made Stone
Rainbow calsilica is a colourful material that was audaciously introduced at the world famous Tucson Gem and Mineral Show in 2002. It quickly attracted plenty of attention but also aroused suspicions about whether it really was a natural stone.
The world's only supplier said he imported rainbow calsilica in large slabs from the state of Chihuahua in Mexico and it was 100% natural but experts were not convinced. As well as renting a large corporate trade-stand that featured blown-up photographs of the mine in Mexico and rough material being extracted, the distributors also printed hundreds of glossy catalogues that went into great detail about this newly discovered material. Someone had certainly invested a huge amount of time, money and effort to try and convince the world that rainbow calsilica was a natural stone.
Despite all the attention that it attracted, when geologists asked to carry out an inspection of the mine their requests were repeatedly denied. The reason they were given was the owners of the land wanted to protect the mine from exploitation so didn't want to reveal its location.
Initial Analysis of Rainbow Calsilica
Analysis that initially took place on rainbow calsilica that had been purchased from the show led some experts to believe it was a cryptocrystalline calcite with various clay minerals acting as bonding agents. Another group of geologists however said it was a man-made material that had been coloured with synthetic colouring agents. The supplier claimed rainbow calsilica had been stabilised with an epoxy in order to increase its durability and that's what's likely to be showing up in the tests. Rocks and minerals are often stabilised to prevent erosion and the process involves filling holes or damaged sections with a resin or other substance. The process is also used for carrying out repairs to some gem-grade stones prior to them being cut and polished.
Despite growing speculation over the authenticity of rainbow calsilica access to the mine continued to be denied but the story about wanting to protect it from exploitation didn't ring true. Were the material to be natural it would have been an extraordinary discovery with the potential to make a significant amount of money and with the mine apparently being on private land, there was no legitimate reason to deny access to experts who wanted to analyse it.
As the supply of rainbow calsilica increased it began appearing at mineral fairs around the world and in the meantime, the rock and mineral community became more determined to find out exactly what this material was. Having inspected a number of different samples one group concluded that it was made up primarily of crushed calcium carbonate which is commonly found in rocks as the minerals calcite and aragonite. It had then been coloured using artificial dyes including PB15 which is a blue pigment and PY1 which is greenish yellow pigment also known as Hansa Yellow. Plastic-like stabilizers had also been used one of which included traces of a paraffin derivative in addition to other chemicals which could not be clearly identified. Traces of the minerals hematite, celestine and calcite were also identified and it seemed many of the particles had been bonded together using a soft plastic-like material similar to paraffin wax.
It has never been discovered exactly who was behind the creation of rainbow calsilica but the idea was both ingenious and audacious. The stone appeared out of nowhere and attracted worldwide attention but this geological hoax was eventually exposed. With that said, rainbow calsilica continues to be widely used as a decorative material despite little being known about those who produce and supply it.
Reference: Kiefert (2003) Rainbow Calsilica, The Journal of the Gemmological Association of Hong Kong 24: 41-46. Third image courtesy of James St. John (Flickr)