An overview is presented of the various vein types, their microstructures and the processes that lead to vein formation. Main modes of transport are diffusional transport, advective or Darcian fluid flow and mobile hydrofractures. Causes for precipitation range from local supersaturation in, for instance, pressure shadows, which is mostly associated with diffusional transport to, often large, supersaturation in externally derived fluids. Variations in fluid pressure between hydrostatic and lithostatic can also cause precipitation of vein material. In general, fibrous textures form due to diffusional transport to low pressure sites, such as pressure shadows.
Fibrous textures can form without brittle fracturing.
Nutrient transport can be by diffusion or by advective fluid flow. Rapid fluid flow, especially in mobile hydrofractures, can bring fluids quickly from their source region to the sites of vein formation, allowing large supersaturation and precipitation of massive amounts of vein material.