Quartz is one of the most frequent minerals and occurs in many different types of rocks. It is one possible modification of SiO2 crystallizing ore: other minerals belonging to the same chemical composition are tridymite, cristobalite, coesite, keatite, stishovite, diatomaceous earth, cryptocristallinic Varieties including glass; for further information see under the headings silica.
Agate, Amethyst, Chalcedony, Cherts, Flint, Onyx, Pure Quartz, Rose Quartz, Silica Flour, Silicic Anhydride.
SiO2 . It is normally weakly contaminated. If Si(4+) is substituted by Al(3+), additional alkali ions (e.g.: Na(+)) are in cluded. Thus, quartz usually contains traces of Li, Na, K, Al, Fe(3+), Mn, and Ti .
a-Quartz is the stable configuration in moderate temperatures (<573° C) and atmospheric pressures. The basic structural elements are SiO4 tetrahedra, which are formed by one silicon atom and four surrounding oxygen atoms. The tetrahedra are bonded to each other by all four oxygen atoms, i.e., one tetrahedron is bonded with four different tetrahedra (chemical formula SiO2) . Additional tetrahedra are grouped and form two different helices: a) a trigonal one, which contains the silicon atoms at levels 0, 1/3 and 2/3 of the unit cell, and b) a hexagonal one, which contains the silicon atoms at levels 0, 2/3, 1/3, 0, 2/3 and 1/3. Only minor differences exist in a-quartz between the natural and theoretical positions of the atoms. a-quartz has a lower symmetry than ß-quartz, which has a stable structure between 573° C and 870° C. The theoretical positions of the atoms are identical to those found in nature. Both structures can be transformed into each other by small variations of the positions of the atoms.
3.350 3.350 3.350 95.600 95.600 95.600.
Trigonal (a-quartz), hexagonal (ß-quartz).
Normally colorless, seldom white, gray, green, or black.
In thin sections, colorless.
3.34 4.26 1.82 1.54 (33-1161).
Cristobalite is stable from 1470° C to 1713° C (melting point) and metastable at lower temperatures.
Similar to tridymite, the cristobalite. Structure is based on layers of six membered rings of tetrahedra. Opposite to tridymite, the triangles belonging to the apical bonding atoms are rotated by 60 between two neighboring layers. The cristobalite structure is open and can accommodate large ions.
4.970 4.970 6.920 90.000 90.000 90.000.
colorless in thin sections.
4.05 2.49 2.84 3.14 (11-695).
Mexico (San Cristobal), and the USA (Yellowstone Park).
Tridymite is stable between 870°C and 1470° C and metastable at lower temperatures.
Identical to quartz. Structure: All tetrahedra in the tridymite structure are bonded to each other and create an open network of six-membered rings. The connected tetrahedra are placed in layers at the bases of the triangles, and the apices point into opposite directions alternately. The apical oxygen atoms are the binding atoms to the next layer. The basic oxygen atoms of one layer are placed directly above those of the underneath layer. The open crystal structure creates channels allowing the passage of large ions.
9.88 17.1 16.3 90.000 90.00 90.000.
nx=1.469-1.477 ny=1.469-1.478 nz=1.473-1.481.
In thin sections, colorless.
4.10 4.32 3.82 2.96.
It is used as a polishing material, in the cement industry, and in the production of silica bricks; for details see under the heading silica.
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United States: ACGIH
United States: NIOSH/OSHA
Crystalline silica have a fibrogenic potency, especially if the quartz particles measure 1-2 µm in diameter. Fibrotic changes of the lung usually develop after an exposure of 20-40 years, and can be classified into three forms; namely simple, complicated, and mixed dust silicosis. For details see under the heading silica.
All silica varieties are possibly fibrogenic; for further information see under the heading silica.
Usually, the symptoms have an insidious onset and include dry cough, shortness of breath during exercise, and progressive dyspnea.
Chest radiographs may be still normal or display fine nodular patterns or dense circumscribed masses without cavitation.
Usually, a combination of restrictive and obstructive changes are noted.
The silica particles can be analyzed in the lavage fluid, for details see under the heading silica.
Several white, grayish or black nodules measuring a few millimeters to a few centimeters in maximum diameter are randomly distributed in both lungs. The hilar lymph nodes are usually black and enlarged, sometimes fibrotic and calcified.
The nodules are composed of concentric acellular collagenous bundles (onion-shaped) which are clearly separated from the adjacent lung parenchyma. Birefringent crystal fibers can be noted in dust-laden macrophages and are usually clustered at the boundary of the nodules. Similar morphological alterations are seen in the hilar lymph nodes, which are, in addition, sometimes calcified. Weak to moderate interstitial inflammatory infiltrates indicate a progressive disease. For details see under the heading silica.
Fair, as a slowly progressive disease is seen in most patients.