Mica is a naturally occurring rock found in specialized mines around the world.  On its own, yes mica is natural. BUT, mica is not usually used in this format when it is used in bath, soap and makeup products. 

Mica is known for its gorgeous bright colours that come along with the shimmer and bling.  The shimmer and bling are naturally occurring when the rock is broken down into tiny dust-like particles.  The colour, however, is not.  The colour that is added to mica in 95% of cases is synthetically produced and adhered to the rock to create the gorgeous colour range we have come to associate with the name "mica".

This product is not dangerous or non compliant to cosmetic manufacturing rules in general.  Some may not be useable in certain areas such as lips due to the colour it contains not being ingestable, but this should be declared in the individual product.  It will still be fine to use elsewhere.

Mica colours are generally not natural, but are still a very colourful option that can be readily used in most soaps, bath products and cosmetics to great effect.