Chemical Weathering in a Tropical Watershed, Luquillo Mountains, Puerto Rico: II. Rate and Mechanism of Biotite Weathering

Murphy, Sheila F.; Brantley, Susan L.; Blum, Alex E.; White, Art F.; Dong, Hailiang

doi:10.1016/s0016-7037(97)00336-0

Cited by 142 publications

(60 citation statements)

References 33 publications

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“…The largest bulk chemical differences relative to the corestone are found in the 7 cm thick protosaprolite zone (Table 1) The average mineralogical composition of the corestone determined by digital point counting is given in Table 2 and is consistent with previous work on the Rio Blanco quartz diorite bedrock (Seiders, 1971;Murphy et al, 1998;White et al, 1998;Turner et al, 2003).…”

Section: Chemical Mobilitysupporting

confidence: 83%

“…Biotite weathering occurs in two stages via two mechanisms. First, an "altered biotite" phase forms that has a larger d (001) spacing, and higher Al/Si and Fe(III)/Fe(II) ratios, and less Fe, Mg, and K than fresh biotite Murphy et al, 1998). This phase was detected in the saprolite, but not in the fresh rock .…”

Section: Field Site and Sample Collectionmentioning

confidence: 99%

“…This phase was detected in the saprolite, but not in the fresh rock . Next, altered biotite weathers to kaolinite in the saprolite either via epitaxial overgrowth of two layers of kaolinite onto one layer of altered biotite or in a 1:1 ratio with the formation of an intermediate halloysite layer Murphy et al, 1998). Within the rindlet zone, plagioclase, hornblende, and chlorite must weather completely because these minerals are not found in the saprolite White et al, 1998;Turner et al, 2003).…”

Section: Field Site and Sample Collectionmentioning

confidence: 99%

“…The agreement of these rates supports the assumption of a steady state regolith profile. Thus, the total denudation rate is commonly equated with the rate of bedrock transformation to regolith for the Rio Icacos watershed and other sites where weathering is assumed to be occurring at steady state (e.g., Murphy et al, 1998;White et al, 1998;Riebe et al, 2003;Turner et al, 2003;Buss et al, 2005;Fletcher et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Weathering of the Rio Blanco quartz diorite, Luquillo Mountains, Puerto Rico: Coupling oxidation, dissolution, and fracturing

Buss

Sak

Webb

et al. 2008

Geochimica et Cosmochimica Acta

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207

146

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Section: Chemical Mobilitysupporting

confidence: 83%

Section: Field Site and Sample Collectionmentioning

confidence: 99%

Section: Field Site and Sample Collectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Weathering of the Rio Blanco quartz diorite, Luquillo Mountains, Puerto Rico: Coupling oxidation, dissolution, and fracturing

Buss

Sak

Webb

et al. 2008

Geochimica et Cosmochimica Acta

Self Cite

207

146

View full text Add to dashboard Cite

“…The BWI is based on the decrease in the quantity of K ions in biotite's interlayer site that occurs during weathering. In general, biotite in slightly weathered granite is partially altered to secondary minerals such as chlorite, vermiculite, and illite, and is completely replaced by kaolinite and goethite in extremely weathered samples [22,24,27,[34][35][36][37]. As shown herein, biotite can survive the early stages of weathering in granite, though does not remain in very strongly weathered granite.…”

Section: Bwi Weathering Index and Compressive Strengthmentioning

confidence: 70%

A preliminary study on the new geotechnical weathering index in the evaluation of altered biotite granite

Choi¹,

Oh²,

Lee³

et al. 2018

IJET

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The existing chemical index of alteration has a difficulty to evaluate the degree of weathering in biotite granites due to an assumption that K2O content decreases along with Na2O, CaO, and MgO. We found that relative K2O content increases during weathering of biotite granite, as it is retained within such rocks due to (1) the chemical and physical stability of K-feldspar and (2) the formation of illite via incorporation of K ions released from biotite. The calculated ranges of most chemical indexes for biotite granite weathering do not show a good correlation with the weathering grade except the CIW, WIP and V indexes. The range of the CIW, WIP and V indexes according to the weathering grade were very small, and thus small errors in whole-rock chemical analyses can produce large discrepancies in calculated values. Further, the WPI index is a relative weathering index that depends on the composition of a fresh standard sample and cannot be applied to determine the absolute degree of weathering in granites if no protolith is available. We suggest a new weathering index (BWI; Biotite weathering index) based on a decrease in the number of K ions in the interlayer site of biotite during weathering of granite.Newly calculated values show a much wider range than the CIW, WIP and V indexes with a good relationship with a weathering grade. Therefore, it is necessary to establish the new index for a detailed classification of weathering degree.

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The chemical, mechanical, and hydrological evolution of weathering granitoid

et al. 2016

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Surprisingly few studies connect the chemical, mechanical, and hydrological evolution of rock as it weathers to saprolite and soil. We assess this coevolution in granodiorite from Monterey Peninsula, California, by measuring changes in bulk chemistry, mineralogy, volumetric strain, the oxidation state of Fe in biotite crystals, tensile strength, abrasion rate, connected porosity, and hydraulic conductivity in samples covering a range of weathering grades. We identify the oxidative dissolution of biotite as the key chemical reaction because of the volumetric expansion that accompanies formation of altered biotite and precipitation of ferrihydrite. We show how the associated accumulation of elastic strain produces an energy density that is sufficient to support rock fracturing over length scales equivalent to constituent crystals. The resulting intragranular and intergranular cracking profoundly reduces tensile strength and increases the abrasion rate, connected porosity, and hydraulic conductivity of the rock matrix. These changes increase the rate of plagioclase weathering, and ultimately the rock disintegrates into grus and clay. Major changes in rock properties can occur with only minor element leaching, and the threshold behavior of weathering that arises from the coevolution of chemical, hydrological, and mechanical properties may be difficult to capture using simplified weathering models that fail to incorporate these properties. Our results, which combine the mechanical and hydrological evolution of weathering rock with more common measurements of chemical changes, should help to more accurately model the effects of, and mechanical and hydrological feedbacks upon, chemical weathering of rock.

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Chemical Weathering in a Tropical Watershed, Luquillo Mountains, Puerto Rico: II. Rate and Mechanism of Biotite Weathering

Cited by 142 publications

References 33 publications

Weathering of the Rio Blanco quartz diorite, Luquillo Mountains, Puerto Rico: Coupling oxidation, dissolution, and fracturing

Weathering of the Rio Blanco quartz diorite, Luquillo Mountains, Puerto Rico: Coupling oxidation, dissolution, and fracturing

A preliminary study on the new geotechnical weathering index in the evaluation of altered biotite granite

The chemical, mechanical, and hydrological evolution of weathering granitoid

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