Rainbow Calsilica is one of the more insidious fakes on the market today.
It exists in a range of colours, shapes, and styles, and is intended to mimic genuine minerals and stones.
The material was originally introduced to the public at the Tucson mineral show of 2002 – limited information was available about the material, and there were many claims of legitimate sources around the world. XRF testing eventually revealed the truth – it is a synthetic material.
It is often comprised partially of natural minerals – typically crushed Calcite, Limestone, and Hematite – however, artificial dyes, resins, and plastics are included too.
Calsilica typically has a Mohs hardness of around 3-4, and scratches easily. The banding is typically too linear to be natural, but it is difficult for the inexperienced to identify the material purely using this method.
It is commonly used to fake Malachite, as quality Malachite is a relatively expensive mineral. It can be very difficult for beginners to identify the difference between it and natural Malachite – however, Malachite is heavy for its size, and cold – due to its metal content. Calsilica has somewhat muted colours, and the banding is often very linear – although it is difficult to use this purely as a diagnostic.
Worth a mention that this is occasionally marketed as fordite, which it is also not, another synthetic material (literally automotive paint overspray) but one with some historical significance in America.