Neutron sources are now part of the large user facilities available to earth scientists, providing not only a broad range of techniques (diffraction, tomography, scattering…), but also giving access to light elements of major interest such as hydrogen. Mineral/rock magnetism is an example for which neutrons have provided unique information on physical properties. The recent progresses in sample environments allow now to perform high P/T investigations to study polymorphic transformations in minerals as well as polymorphism in glasses.