A quartz vein, prominent from the surrounding weathered rock

In geology, a vein is a finite volume within a rock, having a distinct shape, filled with crystals of one or more minerals, which were precipitated from an (aqueous) fluid. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific Water is a common Chemical substance that is essential for the survival of all known forms of Life. FLUID ( F ast L ight '''U'''ser '''I'''nterface D esigner is a graphical editor that is used to produce FLTK Source code Veins are formed by fluids carrying mineral constituents into a rock mass as a consequence of some form of hydraulic flow within the rock. Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion Usually this is the result of hydrothermal circulation. Hydrothermal circulation in its most general sense is the circulation of hot water 'hydros' in the Greek meaning water and 'thermos' meaning heat

Veins are classically thought of as being the result of growth of crystals on the walls of planar fractures in rocks, with the crystal growth occurring normal to the walls of the cavity, and the crystal protruding into open space. A fracture is the (local separation of an object or material into two or more pieces under the action of stress. In Geometry, two lines or planes (or a line and a plane are considered perpendicular (or orthogonal) to each other if they form congruent

This certainly is the method for the formation of some veins. However, it is rare in geology for significant open space to remain open in large volumes of rock, especially several kilometres below the surface. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand Thus, there are two main mechanisms considered likely for the formation of veins: open-space filling and crack-seal growth.

Open space filling

Open space filling is the hallmark of epithermal vein systems, such as a stockwork, in greisens or in certain skarn environments. The neutron temperature, also called the neutron energy, indicates a free neutron's Kinetic energy, usually given in Electron volts The term In Geology, a stockwork is a complex system of structurally controlled or randomly oriented veins. Greisen is a highly altered granitic rock or Pegmatite. Greisen is formed by autogenic alteration of a granite and is a class of endoskarn. Skarn is a Metamorphic rock that is usually variably colored green or red occasionally grey black brown or white For open space filling to take effect, the confining pressure is generally considered to be below 0. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface 5 GPa, or less than 3-5 kilometres. Veins formed in this way may exhibit a colloform, agate-like habit, of sequential selvedges of minerals which radiate out from nucleation points on the vein walls and appear to fill up the available open space. This article is about the semi-precious stone For other uses see Agate (disambiguation. In a woven fabric the selvage (or selvedge) is the uncut edge of the fabric which is on the right- and left-hand edges as it comes out of the Loom Nucleation is the onset of a Phase transition in a small region Often evidence of fluid boiling is present. Vugs, cavities and geodes are all examples of open-space filling phenomenon in hydrothermal systems. Vugs are small to medium-sized cavities inside rock that may be formed through a variety of processes Geodes ( Greek geoides, "earthlike" are geological rock formations which occur in sedimentary and certain Volcanic Hydrothermal circulation in its most general sense is the circulation of hot water 'hydros' in the Greek meaning water and 'thermos' meaning heat

Alternatively, hydraulic fracturing may create a breccia which is filled with vein material. Hydraulic fracturing is a method used to create fractures that extend from a Borehole into Rock formations which are typically maintained by a proppant Breccia (ˈbrɛtʃiə ˈbrɛʃiə breach is a rock composed of angular fragments of several Minerals or rocks in a matrix, that is a cementing material Such breccia vein systems may be quite extensive, and can form the shape of tabular dipping sheets, diatremes or laterally extensive mantles controlled by boundaries such as thrust faults, competent sedimentary layers, or cap rocks. Strike and dip refer to the orientation or attitude of a Geologic feature A diatreme is a breccia filled Volcanic pipe that was formed by a gaseous explosion A thrust fault is a type of fault, or break in the Earth's crust with resulting movement of each side against the other in which a lower stratigraphic position is pushed up Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes

Crack-seal veins

When the confining pressure is too great, or when brittle-ductile rheological conditions predominate, vein formation occurs via crack-seal mechanisms. Ductility is a mechanical property used to describe the extent to which materials can be deformed plastically or "stretched" into "wires" without In Geology, a rheid is a Solid material that deforms by viscous flow

Crack-seal veins are thought to form quite quickly during deformation by precipitation of minerals within incipient fractures. In Materials science, deformation is a change in the shape or size of an object due to an applied force. Precipitation is the formation of a Solid in a Solution during a Chemical reaction. This happens swiftly by geologic standards, because pressures and deformation mean that large open spaces cannot be maintained; generally the space is in the order of millimetres or micrometres. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre Veins grow in thickness by reopening of the vein fracture and progressive deposition of minerals on the growth surface.

Tectonic implications

Veins generally need either hydraulic pressure in excess of hydrostatic pressure (to form hydraulic fractures or hydrofracture breccias) or they need open spaces or fractures, which requires a plane of extension within the rock mass. Fluid statics (also called hydrostatics) is the Science of Fluids at rest and is a sub-field within Fluid mechanics.

In all cases except brecciation, therefore, a vein measures the plane of extension within the rock mass, give or take a sizeable bit of error. Measurement of enough veins will statistically form a plane of principal extension.

In ductilely deforming compressional regimes, this can in turn give information on the stresses active at the time of vein formation. Stress is a measure of the average amount of Force exerted per unit Area. In extensionally deforming regimes, the veins occur roughly normal to the axis of extension. In Mathematics and its applications a coordinate system is a system for assigning an n - Tuple of Numbers or scalars to each point

Mineralisation and veining

Figure 1.
Boudinaged Quartz vein(with strain fringe) showing sinistral shear sense. boudinagejpg|thumb|Boudinaged Jasperoid in sheared basalt Fortnum Gold Mine Australia Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in This article is about the geologic usage for human physiology usage see the articles Laterality. Study of geological shear is related to the study of Structural geology, Rock microstructure or rock texture and fault mechanics. Starlight Pit, Fortnum Gold Mine, Western Australia. Western Australia is a state occupying the entire western third of the Australian continent.

Veins are of prime importance to mineral deposits, because they are the source of mineralisation either in or proximal to the veins. Typical examples include gold lodes, as well as skarn mineralisation. Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 In Geology a lode is the metalliferous Ore that fills a Fissure in a rock or a vein of ore deposited between layers of Skarn is a Metamorphic rock that is usually variably colored green or red occasionally grey black brown or white Hydrofracture breccias are classic targets for ore exploration as there is plenty of fluid flow and open space to deposit ore minerals. An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining

Ores related to hydrothermal mineralisation which are associated with vein material may be composed of vein material and/or the rock in which the vein is hosted.

Gold-bearing veins

In many of the gold mines exploited during the gold rushes of the 19th century, vein material alone was typically sought as ore material. A gold rush is a period of feverish migration of workers into the area of a dramatic discovery of commercial quantities of Gold. In most modern mines, ore material is primarily composed of the veins and some component of the wall rocks which surrounds the veins.

The difference between 19th century and modern mining techniques and the type of ore sought is based on the grade of material being mined and the methods of mining which are used. Historically, hand-mining of gold ores permitted the miners to pick out the lode quartz or reef quartz, allowing the highest-grade portions of the lodes to be worked, without dilution from the unmineralised wall rocks.

Modern mining using larger machinery and equipment forces the miners to take low-grade waste rock in with the ore material, resulting in dilution of the grade.

However, modern mining and assaying allows the delineation of lower-grade bulk tonnage mineralisation, within which the gold is invisible to the naked eye. In these cases, veining is the subordinate host to mineralisation and may only be an indicator of the presence of metasomatism of the wall-rocks which contains the low-grade mineralisation. In Music alteration, an example of Chromaticism, is the use of a neighboring pitch in the Chromatic scale in place of its Diatonic neighbor such

Gold Bearing Quartz Veins, Blue Ribbon Mine, Alaska

For this reason, veins within hydrothermal gold deposits are no longer the exclusive target of mining, and in some cases gold mineralization is restricted entirely to the altered wall rocks within which entirely barren quartz veins are hosted.

See also

• Boudinage
• Ore genesis
• Shear (geology)