Many calcites look as if someone has sketched over their surface to add a dimension of human endeavour to a natural masterpiece.
Calcite can be transparent or opaque and occasionally shows phosphorescence, and a transparent variety is used for optical purposes. Experiments have even been conducted using calcite as a cloak of invisibility - but it has been difficult to see the results.
More relevantly, here we have an intriguing "natural artwork" with wonderful bands of colour that would make many artists proud.