Quartz, cryptocrystalline

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. 

The cryptocrystalline quartz has cells which are in different orientation in the particle and the shadow effect of light passing between cell boundaries causes the granular appearance. 

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. 

SYNS ACCUSAND amorphous quartz AMORPHOUS SILICA BORSIL P CRYPTOCRYSTALLINE QUARTZ DENKA F 90 DENKA FB 44 ... 

T errazzo Framework of c. 60% quartz grains, with solution cavities, in a cryptocrystalline quartz or opaline matrix with colloform banding conchoidal fracture typical... 

Albertinia Detrital quartz absent or rare, cryptocrystalline quartz matrix of terrazzo type... 

Chert A cryptocrystalline quartz with sub-microscopic crystal size and impurities that give it color and cloudiness. 

SYNONYMS amorphous quartz, amorphous silica, cryptocrystalline quartz, fused quartz, fused silica, fuselex, microcrystalline quartz, quartz, glass, quartz sand, silicon dioxide, silicone dioxide, suprasil, vitreous silica. 

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. 

Cryofluoran Cryofluorane. See 1,2-Dichlorotetrafluoroethane Cryolite. See Sodium fiuoroaluminate Cryptocrystalline quartz. See Silica, fused Cryptoxanthin. See Kryptoxanthin Crystal 78, Crystal 82. See Sodium silicate Crystal O Crystal P, Crystal Crown LP, Crystal Crown. See Castor (Ricinus communis) oil... 

CAS 60676-86-0 EINECS/ELINCS 231-545-4 Synonyms Amorphous quartz Amorphous silica Cryptocrystalline quartz Fused quartz Fused silica... 

According to Patton (1973a, b), the designation amorphous is a misnomer since it is actually cryptocrystalline quartz that is, one where the crystallite size is so fine that it is invisible under light microscopy. 

A form of quartz with abnormal thermal properties occurs frequently in New Zealand soils (Fieldes [1952] Fieldes and Swindale [1954]). This silica polymorph has the X-ray diffraction pattern of a-quartz, but the differential thermal analysis curves does not show the a-j3 inversion effect. Although its refractive index is lower than that of chalcedony, it has many features in common with cryptocrystalline quartz, and hence has been termed chalcedonite (Fieldes and Swindale [1954]). Since it tend to be concentrated in the fine clay fraction, it is thought to be of secondary origin crystallizing from amorphous silica, an initial product in the weathering of volcanic ash soils. The silica in fossilized wood has been shown to have properties very similar to chalcedonite (Keith and Tuttle [1952]). 

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