English: "Rainbow calsilica" is man-made material attributed to Mexico (?) that consists of irregular, colorful layers. It is intended to imitate "fordite", which is an artificial material composed of numerous layers of car paint.

Stories have been invented to explain the origin of this material (for example, semi-natural sedimentary layers derived from an old tile-making plant).

Chemical analysis has shown that there is nothing natural about these colorful layers. The bulk of rainbow calsilica is crushed calcium carbonate rock. Artificial dyes have been added (e.g., the blue is from a post-1930s pigment called PB15 and the greenish and yellowish bands contain a pigment called PY1, or Hansa Yellow).

Plastic-like stabilizers have also been added - aliphatic polymers or a paraffin derivative, plus other undetermined chemicals.

I like to call artificial stones "rock-us fake-us". They can be attractive, so I don't have a problem with them. I do have a problem with scammers lying about the origin of such materials.

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Chemical info. from:

Kiefert (2003) - "Rainbow calsilica". The Journal of the Gemmological Association of Hong Kong 24: 41-46.