Titanium Dioxide, a common component used in micas to add opacity and color, carries a Proposition 65 warning in its powdered form.
While it appears on the Proposition 65 warning list, it only requires a warning when in powdered form. Once the mica that includes titanium dioxide is suspended in a liquid or solid base, like a soap, it no longer requires a Prop 65 warning. Not all micas contain titanium dioxide, so it is important to check the ingredients list on the product details page if your finished product will be a powder.
For more information, check out the Proposition 65 page for Titanium Dioxide here: Proposition 65 Titanium Dioxide Warning