Cryptocrystalline mineral

Texture. All limestones are crystalline, but there is tremendous variance in the size, uniformity, and arrangement of their crystal lattices. The crystals of the minerals calcite, magnesite, and dolomite are rhombohedral those of aragonite are orthorhombic. The crystals of chalk and of most quick and hydrated limes are so minute that these products appear amorphous, but high powered microscopy proves them to be cryptocrystalline. Hydrated lime is invariably a white, fluffy powder of micrometer and submicrometer particle size. Commercial quicklime is used in lump, pebble, ground, and pulverized forms. 

Quartz is found in several forms in all three major kinds of rocks—igneous, metamorphic, and sedimentary. It is one of the hardest minerals known. Geologist often divides quartz into two main groupings—course crystalline and cryptocrystalline quartz. Course crystalline quartz includes six-sided quartz crystals and massive granular clumps. Some colored varieties of coarse crystalline quartz crystals, amethyst and citrine, are cut into gem stones. 

Most commonly, zeolites are found in series of sedimentary rocks which contain pyroclastic material and are formed during the devitrification of this material. If the rocks are silica-rich, the zeolite species formed seems dependent upon the bulk composition and burial depth or temperature of formation (Hay, 1966). They are most frequently accompanied by silica in an amorphous or cryptocrystalline form (opal, chalcedony). Analcite and all other compositional intermediates up to the silica-rich clinoptilolite are found in this association. The most comifton clay mineral in such tuffs is montmorillonite. Zeolites are sometimes found with glauconite (Brown, et al . 1969) or celadonite (Hay, 1966 Iijima, 1970 Read and Eisenbacher, 1974) in pelitic layers or acidic eruptive rocks... 

In renal stones, apatite (Ca5(P04)3 OH, 1/2 C03) with a hexagonal shape has been observed however, this mineral is difficult to identify because of its cryptocrystalline appearance. Struvite (MgNH4P04 6 H20) orthorhombic, newberyte (MgHP04 3 H20) orthorhombic, whit-ockite (Ca3(P04)2) hexagonal, and also brushite have been reported to occur in renal stones82. ... 

Next to materials of the glass-ceramics type, many varieties of chalcedony, such as agate, carneol, onyx, sardonyx, heliotrope and jasper, exhibit similar changes in hardness resulting from different consolidation of the cryptocrystalline structure of silica among mineral individuals. 

It was stated that hydrated calcium monohydrogen phosphate in amorphous or cryptocrystalline form is a potential precursor in the formation of hydroxyapatite because the structural position of Ca2+ on (010) and (110) crystal planes of both minerals essentially correspond to one another492. These planes of calcium ions could easily serve as transition boundaries with little distortion of crystal structure the same holds true for octacalcium phosphate or defect apatites. Thus apatite may form from amorphous or microcrystalline calcium monohydrogen phosphate possible via octacalcium phosphate or defect apatites. This process may already start inside the matrix vesicles and continue during extravesicular activities. 

Flint is a common name applied to any material, rock or mineral, that is composed mostly of massive cryptocrystalline quartz. This word is usually used to describe dark-colored chert nodules found in limestones. The term flint is often used by anthropologists to describe homogeneous siliceous materials that have been used to make tools or weapons, regardless of their actual composition. 

We have worked out a sufficiently precise and reliable system of consistent thermodynamic constants (Mel nik, 1972) especially for analysis of the conditions of formation of iron ores. In this work, in addition to the constants of crystalline minerals, data on the stability and thermodynamic properties of the original finely dispersed amorphous or cryptocrystalline iron, magnesium, and silica sediments were systematized for the first time. Such sediments are metastable solid phases which in nature are converted into stable crystalline minerals during diagenesis and low-rank metamor-... 

Cryptocrystalline natural graphite is also beneficiated using flotation, but this is complicated by its small particle size and the resulting more homogeneous distribution of the accompanying minerals. Oils are preferred as flotation media. 

The composition of pure quartz is close to 100% pure Si02 because the structure of the mineral is so compact and perfect that there is no room for silica replacement by any other element. Also, quartz is insoluble in all acids except HF, which further contributes to its purity. Quartz forms many micro- and cryptocrystalline varieties. Some of them are well-known as semiprecious stones (amethyst, citrine, agate, tiger-eye, etc.). 

Crystalline apatite meets all of these criteria extremely well, particularly the last which is a vitally important, but often under-appreciated, factor for any mineral to achieve widespread application. Many other minerals have been the subject of overly optimistic reports on their suitability for fission track dating but fail meet one or more of these requirements and so are limited in their application. For example, cryptocrystalline... 

H—Hardness. There are different types of hardness. Why Because the value of a material s hardness depends on how it is tested. The hardness of a material is its resistance to the formation of a permanent surface impression by an indenter. You will also see it defined as resistance of a material to deformation, scratching, and erosion. So the geometry of the indenter tip and the crystal orientation (and therefore the microstructure) will affect the hardness. In ceramics, there tends to be wide variations in hardness because it involves plastic deformation and cracking. Table 16.4 lists hardness values on the Mohs hardness scale, a scratch test that can be used to compare hardness of different minerals. For example, quartz has a Mohs hardness of 7, which made flint (a cryptocrystalline quartz) particularly useful in prehistoric times for shaping bone (the mineral component is apatite with hardness 5) and shell (the mineral component is calcite with hardness 3). Mohs hardness scale was not the first scratch hardness technique. As long ago as 1690, Christian Huygens, the famous astronomer, had noticed anisotropy in scratch hardness. 

Gravel can provide the harmful components, for example chalcedoity (mentioned above), cryptocrystalline quartz or dolomite with the clay minerals inclusions. The magnesium anthophyllite can be reactive too. 

When a mineral is produced in favourable condition, its ordered internal strueture is reflected in its external morphology and the mineral has a c/yxto/// e form. Otherwise a mineral is cryptocrystalline, i.e. the crystalline form is not perceptible externally but can be detected by scientific analyses like X-Ray Diffraetion. Amorphous natural solids like coal, volcanic glasses etc. do not qualify as minerals. 

Most of the solid components of the Earth s crust, i.e. rocks, sediments, clays etc. are largely made up of various mineral species. Amineral species is deiined as A naturally occurring, inorganic, homogeneous solid, having a definite (but not necessarily fixed) chemical composition and a fixed ordered internal structure, i.e. crystalline. This ordered internal structure is reflected in the external morphology when the mineral has a well crystalline form. When the crystalline form is not perceptible externally called cryptocrystalline, its crystalline nature can be detected by scientific analytical techniques like X-Ray Difiraction. Amorphous natural solids like coal, volcanic glasses etc. do not qualify as minerals. The abimdance of any mineral in the Earth is decided by the availability of the constituent elements of the mineral in the earth s crust and also the stability of that mineral in the surface or near-surface environment. 

The foregoing minerals are varieties of quartz. Opal is a cryptocrystalline variety of cristobalite, somewhat hydrated. The striking colors of opal are caused by Bragg diffraction (Appendix IV) of visible light by spheru-lites of cristobalite about 300 nm in diameter that have settled into a close-packed array and have been cemented together by a silicious cement with index of refraction different from that of the spherulites. 

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