Talc
Talc is a mineral composed of 31.7% magnesium oxide (MgO), 63.5% silicon dioxide (SiO2) and 4.8% water. It is formed by the alteration of dolomite or ultramafic IGNEOUS rocks. A formula for pure talc would look like this: 3 dolomite + 4 quartz + 1 water = 1 talc + 3 calcite + 3 CO2.