Feldspar rhyolite

Nevada K-feldspar, rhyolite vitrophyre 18.18 15.69 39.42 This paper (Table 19) ... 

Figure 12 continued, (d)-(g) Mineral isochrons for rhyolites from the Olkaria volcanic center (Kenya), (d) and (f) alpha spectrometry resnlts from Black et al. (1997). (e) and (g) TIMS resnlts from Henmaim and Davies (2002). All the rhyolites have eraption ages between 3.3 and 9.2 ka. Note that the same sample (570) analyzed in both stndies gives rather different ages (f and g). Same abbreviations of mineral names as in Fignre 10 + Qz qnartz KF alkali feldspar Amph amphibole Bt biotite. 

Potassium feldspar (orthoclase) Muscovite mica Quartz Felsic (rhyolite granite)... 

The plot of 5 0 versus the integrated, water/rock ratio (e.g., Criss Taylor 1986) in Figure 1 graphically describes isotopic alteration of two model rock types, andesite (A, primary 5 0 = 6.0 %o) and rhyolite (R, primary 5 0 = 7.0 %o), simply modeled by feldspar-seawater (5 Osw = 0.0 %o), over a wide range of water/rock... 

Lake to just south of where the Victoria River empties into Red Indian Lake (Fig. 1). Light grey-green to white, dacitic to rhyolitic quartz-feldspar-porphyritic... 

Aphyric to sparsely feldspar-phyric rhyolite flows, associated breccias and related hyalotuffaceous sedimentary rocks of the FLB Formation, and basaltic and related sedimentary rocks of the LR Formation immediately overlie the exhalitive (sulfides and iron-formation) horizon of the Key Anacon East and the Key Anacon Main Zones, respectively (van Staai etal. 2003). 

In the JRS the Dalhousie Group is divided into five formations (Walker and McCutcheon 1995). Only the upper three Archibald Settlement, Sunnyside and Big Hole Brook formations (described below), are exposed in the vicinity of Nash Creek. The Archibald Settlement Formation is the lowermost of these and consists of massive flows and domes of orange to red, aphyric, commonly flow-layered rhyolite. Up section massive flows are interlayered with fine- to coarse-grained volcaniclastic rocks including heterolithic lapilli-tuff and agglomerate, as-well-as volumetrically minor feldspar-phyric rhyodacite. A U/Pb zircon age of 415.6 +/-0.4 Ma has been returned from rhyolite of... 

Volcanic rocks of more intermediate composition are rare in the TCZ but are present at both the Nash Creek and Sewell Brook deposits. At Nash Creek, feldspar-phyric rhyodacite containing 500 ppm Zr immediately overlies low-Zr rhyolite and likely reflects draw-down in a small, zoned magma chamber. At Sewell Brook, most of the volcanic rocks in the immediate vicinity of the deposit are rhyodacitic in composition. 

Pavlish, L. A. Sheppard, P. J. Hancock, R. G. V. NAA A Method of Determining Feldspar Types and Their Mixtures in Fine-Grained Rhyolites. Paper presented at the workshop Analytical Tools in Archaeometry 1 Oct. 7-9, 1985, Newark, Delaware. 

White J. C. (2003) Trace element partitioning between alkali feldspar and peraUcalic quartz trachyte to rhyolite magma Part 11. Empirical equations for calculating trace element partition coefficients of large-ion lithophile, high field strength and rare-earth elements. Am. Mineral. 88, 330-337. 

Rhyolite Igneous Fine-grained, homogeneous, with Feldspar, mica, quartz... 

Feldspars are common aluminosilicate minerals that are present in many different igneous rocks including granites and rhyolites [11], When exposed, these rocks are susceptible to physical and chemical attack. Water, along with the sun, plant roots, and other forces physically attack rock formations causing crevice formation and fracture [3], Water also attacks rocks chemically. Over time, anhydrous aluminosilicate compounds such as those present in igneous minerals react with water to form hydrated species [20], The classic chemical reaction for clay formation involves the decomposition of potash feldspar due to the action of water-containing dissolved C02 to form kaolinite (insoluble) and soluble ionic species (Reaction 1) [14],... 

Sa.7.2.64) Rhyolite plug (about 30 m in diameter) intruding the Patuxent Formation, Williams Hills. K-feldspar phe-nocrysts (15%) in an aphanitic groundmass. 

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