Antigorite

Antigorite is a silicate rich in magnesium derived from ultrabasic igneous rocks. It is part of the asbestos family but is also associated with muscovite (golden mica) which gives it its golden yellow colour. Its crystalline form, which is both fibrous and lamellar due to the mixture of asbestos and muscovite, is rarely observable because it is usually in massive form, i.e. in clusters of very small crystals.