Minerals fracture

However, most minerals fracture rather than cleave. Fracture is breakage that does not follow a flat surface. Some fracture surfaces are rough and uneven. Others show smooth, concentric depressions, called conchoidal fractures. Conchoidal fracture typically occurs in glasses, which are non-crystalline solids. However, it also occurs in many common crystalline minerals, for example garnet and quartz. 

Non-carious cervical lesions of the tooth are typically wedge-shaped and show loss of tooth tissue mainly on the buccal surfaces of the tooth close to the cemento-enamel junction. This is the case, regardless of the tooth affected [72]. When the tooth is loaded asymmetrically, there are typically flexing stresses, and these produce tension on one side of the tooth and compression on the other. Both types of force are located close to the cemento-enamel junction [86], The result is that tooth mineral fractures in this region, and falls away, causing a non-carious lesion to develop. These lesions typically involve exposure of the dentine [72]. 

Bird DK, Rogers RD, Manning CE (1986) Mineralized fracture systems of the Skaergaard intrusion. Medd Gronland Geosci 16 1-68... 

The nature of the atoms forming the mineral, the forces between them and their order determine its fundamental properties such as chemistry, density, optical properties, hardness and shape. They will also determine the mechanisms by which minerals fracture and thus play a strong role in determining shape, size and size distribution. 

Mercury ore deposits occur in faulted and fractured rocks, such as limestone, calcareous shales, sandstones, serpentine, chert, andesite, basalt, and rhyolite. Deposits are mostiy epithermal in character, ie, minerals were deposited by rising warm solutions at comparatively shallow depths from 1—1000 m (6). 

The oil industry uses microencapsulated oil-field chemicals. For example, microencapsulated breaker is deHvered into a subterranean formation where it breaks the fracturing Hquid used to stimulate the recovery of fluids such as cmde oil or natural gas. Examples of breakers encapsulated include oxidi2ers, en2ymes, and various mineral or organic acids. 

Deposits which are forming are frequentiy characterized by venting streams of hot (300°C) mineralized fluid known as smokers. These result in the local formation of metalliferous mud, rock chimneys, or mounds rich in sulfides. In the upper fractured zone or deep in the rock mass beneath the vents, vein or massive sulfide deposits may be formed by the ckculating fluids and preserved as the cmstal plates move across the oceans. These off-axis deposits are potentially the most significant resources of hydrothermal deposits, even though none has yet been located. 

Almost two-thirds of the world s copper resources are porphyry deposits. The term porphyry is generally appUed to a type of disseminated copper deposit that is hydrothermal in origin and characterized by a large proportion of minerals uniformly distributed as disseminations or in fractures and small veins. Copper contents are generally 1% or less. The most extensive porphyry deposits are located in western Canada, the southwestern United States, Mexico, and western South America. In addition to the porphyrys, there are large bedded copper deposits in Germany, Poland, the CIS, AustraUa, and central Africa. 

Here is the number of cycles to fracture under the stress cycle in region i, and Nj/Nf is the fraction of the lifetime used up after N, cycles in that region. Failure occurs when the sum of the fractions is unity (eqn. (15.4)). This rule, too, is an empirical one. It is widely used in design against fatigue failure but if the component is a critical one. Miner s Rule should be checked by tests simulating service conditions. 

Plutonium is transported by the groundwater in fractures in the rock (usually <1 mm wide). A typical groundwater velocity (vw) at >100 m depth in Swedish bedrock is 0.1 tn/y. The fractures are filled with crushed, weathered, clayish minerals, which have a high capacity to sorb the plutonium. Assuming instantaneous and reversible reactions, the sorption will cause the plutonium to move considerably slower (with velocity vn) than the groundwater. The ratio between these two velocities is referred to as the retention factor (RF), defined by... 

Thermal expansion induced by insolation may be important in desert areas where rocky outcrops and soil surfaces are barren. In a desert, daily temperature excursions are wide and rocks are heated and cooled rapidly. Each type of mineral in a rock has a different coefficient of thermal expansion. Consequently, when a rock is heated or cooled, its minerals differentially expand and contract, thereby inducing stresses and strains in the rock and causing fractures. Ollier (1969) discussed examples of rock weathering due to insolation. Fire can develop temperatures far in excess of insolation and be quite effective in fracturing rocks (Black-welder, 1927). 

---