Rainbow Calsilica Stone



close up of the layers in the man-made stone known as rainbow calsilica 

Rainbow Calsilica | Man-Made Stone

Rainbow calsilica is a unique and colourful material that was audaciously introduced at the world famous Tucson Gem and Mineral Show in 2002. It quickly attracted plenty of attention but some were suspicious about whether it was really a natural stone. 

The world's only supplier of rainbow calsilica said it was imported in large slabs from the state of Chihuahua in Mexico and was 100% natural but experts were not convinced.  As well as renting a large corporate trade-stand full of large photographs of the mine and rough material being extracted, professionally printed catalogues about this newly discovered material were also distributed.  Someone had invested an incredible amount of time, money and effort to try and convince the world that rainbow calsilica was natural yet when different groups of geologists asked to carry out an inspection their requests were repeatedly denied.  The reason was apparently because the owners of the land wanted to protect the mine from exploitation so didn't want to reveal its location.


rectangular shaped rainbow calsilica stone


The Initial Analysis of Rainbow Calsilica

Analysis that initially took place on stones that had been purchased led some experts to believe it was a cryptocrystalline calcite with various clay minerals acting as bonding agents but another group of geologists said it was man-made and had been coloured with synthetic colouring agents. The supplier claimed that 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 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 material prior to it 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 this to be a natural rock 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.



slab of the man-made stone rainbow calsilica



As the supply of rainbow calsilica increased it began appearing at mineral fairs around the world and in the meantime the scientific 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 a common substance 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 which was likely to be something 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 plenty of attention from around the world but this geological hoax was eventually exposed.  With that said, the stone continues to be widely used as a lapidary material despite so 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)



Rainbow Calsilica Necklace Pendants


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