Despite the approval of certain mica-based pigments for food use, concerns continue to arise regarding their safety. One primary issue is related to heavy metals that can sometimes be found in natural mica. For example, if the mica is derived from contaminated sources, it could potentially introduce elements like lead or arsenic into the food supply, raising health concerns. It is crucial for manufacturers to source their mica from reputable suppliers who perform thorough testing to ensure its purity.

The mica variety that does not contain iron is colorless in flakes, and the higher the iron content, the darker the color, and the more polychromatic and absorbable it is. According to the different chemical composition and optical characteristics, mica group minerals can be divided into Muscovite subgroup, biotite-phlogopite subgroup and lemica subgroup. The common mica are biotite, phlogopite, Muscovite and so on.

A group of parallel cleavages can be seen in a photograph of biomica under orthogonal polarized (left) and single polarized (right) mirrors.