Mineral vein

A fracture filled by minerals precipitated from a fluid. Quartz and calcite are common examples. Growth textures and cross-cutting relations can constrain opening and fluid-flow history, but mineral filling alone does not establish whether the fracture also experienced fault slip.

A fluid-filled fracture can open perpendicular to the least compressive principal stress. In a compression-positive contact approximation, effective stress is ${\sigma }_n^{\prime }={\sigma }_n-P_f$. Opening an initially intact plane of tensile strength $T_0$ requiresA sufficiently weak pre-existing crack can open near zero effective compression. Increasing isotropic pore fluid pressure translates all effective principal stresses without rotating their directions, so an opening fracture and a frictional normal fault can record compatible stress axes at different pressure episodes. Subsequent mineral precipitation creates a mineral vein; white appearance alone does not identify its filling mineral.