Crystal Growth and Intracrystalline Zonation Patterns in Hydrothermal Environments

Fluid flow through porous or fractured rocks is commonly associated with mineral growth and dissolution processes along the flow path. Precipitation of ore minerals from hydrothermal fluids is responsible for the generation of the world’s most important class of ore deposits (Skinner, 1969). Hydrothermal systems also provide some of the most spectacular examples of naturally grown mineral crystals, which occasionally may reach a size of several centimeters and even decimeters. Growth of large crystals can only take place in a system with efficient supply of nutrients either through dissolution of other minerals in the local environment or by advective mass transport and external supply of chemical components associated with large-scale flow of the hydrothermal fluid. An additional requirement is that the crystal grows in a’soft’ environment such as a fluid filled pore space or in a rock matrix which allows the growing mineral to develop a shape that minimizes the surface energy of that particular grain, i.e. a faceted crystal. This is generally not the case in rocks with low porosity where the total surface energy of the whole society of grains (the rock) determines the shape of the individual grains.