High quartz

The Dauphine twins of quartz are formed when quartz is transformed from its high-temperature form (p or high quartz, stable above of 573 °C) to the low-temperature form... 

A circulating fluidized bed (CFB) photoreactor and installation of the UV light lamps is shown in Fig. 1. The CFB photoreactor composed of a riser (13 mm-i.d. x 1200mm-high, Quartz glass), cyclone, downcomer... 

Hexagonal trapezohedron, hexagonal dipyramid, dihexagonal prism, hexagonal prism, pedion High quartz... 

TrT.oo 10 79 250 K(high quartz high cristobalite) 1996 5 K(high cristobalite liquid)... 

The enthalpy of formation is calculated from that of quartz using Aj.H (970 K) 0.45 0.15 kcal mol" for high quartz high cristobalite, as determined by Holm (1 ) from is an oxide melt. This value reduces to A H (298.15 K) = 0.60 kcal mol for... 

The melting point of high cristoballte is 1996 i 5 K, while the metastable melting point of high quartz is 1696 A gH is the difference between Aj,H for liquid and high cristoballte at T. Values ranging from 1.8 to 3.6 kcal mol been derived from various interpretations of phase diagrams (1 ). 

The rates of these reactions, which represent only part of the very complex chemical processes involved, are diffusion limited. By varying the firing temperature and firing time, articles can be obtained either with very high tran.sparency due to almost complete dissolution of the crystalline phases or with high mechanical strength with high quartz contents. 

Schulz H, Tscheny V (1972a) Stractural relations between the low- and high-temperature forms of P-euciyptite (LiAlSi04) and low and high quartz. 1. Low-temperature form of p-eucryptite and low quartz. Acta Crystallogr B28 2168-2173... 

Mineralogic Composition. The subject shales are designated silty shales due to their high quartz content. The mineralogic composition of these shales has been studied (14-18) and is summarized in Table III. Illite (2M), muscovite and/or illite/smec-tite are the predominant clays found in these shales. 

Quartz. In this seam, quartz content tends to be relatively low, with many samples containing less than 15% (Figure 3). High quartz contents (15-20% and above) are observed in the north-central part of the region, in Clarion and Jefferson Counties, and in several isolated areas along the eastern edge of the field area, such as Centre County. Low quartz contents occur in a zone extending from the south and southeast towards the northwest, and in Clearfield County. 

The Lower Kittanning coal contains kaolinite (well-crystallized), illite/mica and expandable clays. Low total clay contents are observed in the center of the study area, where the coal is rich in pyrite, and in the north-central region where high quartz contents are observed. High total clay contents are seen on the northwestern and eastern margins of the basin. Because clay mineral data are presented as a percentage of the low-temperature ash, variations in the quartz and pyrite contents influence the proportionate distribution of the clays. To avoid this problem, the relative amounts of individual clay minerals in the clay (less than 2 micron) fraction were examined. As this size fraction contains only clays, variations in quartz and pyrite do not influence the results. 

The relatively high quartz contents observed towards the north of the study area reflect the influx of quartz-rich detritus from a topographic high in that area. Most of the detritus entering the basin from the east was clay-rich however, local influxes of quartz may have occurred periodically. 

Data have been subdivided by petrographically defined mineral proportions. High quartz content samples are those with greater than 80% quartz, medium quartz content samples have between 60 and 80% quartz, low quartz content samples have less than 60% quartz. 

---