Garnet and quartz

Reactions 12 and 13. The coexistence of plagioclase, orthopyroxene, garnet, and quartz may be expressed as an equilibrium involving ferrous and/or magnesian components, as seen in the preceding case ... 

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. 

Associated minerals include other clays, garnets, biotite and quartz. 

Goldman D. S. and Albee A. L. (1977). Correlation of Mg/Fe partitioning between garnet and biotite with 0/ 0 partitioning between quartz and magnetite. Amer. Jour. Set, 277 750-767. 

Microscopically, the BIF is composed mainly of iron oxide rich bands that alternate with microcrystalline silica bands, quartz, chert and jasper. The ratios of these constituents are different from one sample to another. Occasionally, the samples contain sulfides, garnet and graphite. 

Garnet and cordierite blastesis postdating S1/S2 fabric contain inciusion traiis of quartz, biotite and phengitic micas and indicate the influence of a iate thermai overprint due to intrusion of the Pabineau Granite. 

Several refractory accessory mineral thermometers have been applied, including aluminosilicate, magnetite, garnet and rutile in quartz-rich rocks and magnetite,... 

When comparing ionic porosity of different minerals, for self-consistency, the same set of ionic radii should be used, and the same temperature and pressure should be adopted to calculate the molar volume of the mineral. Table 3-3 lists the ionic porosity of some minerals. It can be seen that among the commonly encountered minerals, garnet and zircon have the lowest ionic porosity, and feldspars and quartz have the highest ionic porosity. More accurate calculation of IP may use actual X-ray data of average inter-ionic distance and determine the ionic radius in each structure. 

The second provenance criterion is based on the identification of inclusions in gemstones. Micro-Raman spectrometry was used for this task in almandine garnets. Various inclusions were observed like apatite, zircon, monazite, calcite, and quartz and two of them, curved needles of sillimanite (Al2Si05) and 10-pm metamict radioactive crystals, were specifically found in archaeological garnets. Fig. 6 shows the Raman spectra of a sillimanite needle, which is a mineral formed under a high temperature and high pressure metamorphism. 

P-T conditions are ordinarily calculated based on the T-dependence of a cation partitioning equilibrium (e.g., Fe-Mg exchange between garnet and biotite), and the F-dependence of a net-transfer equilibrium (e.g., anorthite = grossular + aluminosilicate -h quartz). Most barometers have moderate slopes, so the calculated P depends moderately on T. The basic problem... 

Hornfels—metamorphic rock containing micas, quartz and garnets and that is formed from clay-rich rocks. 

Modal spaces for some common pelitic schist assemblages characteristic of the lower grades of metamorphism will be presented below. The minerals involved will be quartz, dioctahedral mica, trioctahedral mica, chlorite (14-., garnet, and chloritoid. The formulas of the additive components for these will, to save space, be written in the equations as Qtz, Dim, Bio, Chi, Gar, and Ctd, respectively. The additive components may then all be chosen so as to lie in the space defined by K20-Mg0-Al203-Si02-H20, as follows ... 

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