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How brucite may affect the frictional properties of serpentinite

Open-File Report 2001-320
By: , , , , and 
https://doi.org/10.3133/ofr01320

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Abstract

The frictional strength of brucite gouge has been measured at hydrothermal conditions to 450°C. At room temperature, brucite has a coefficient of friction, μ ≈ 0.30, making it one of the weakest minerals identified to date. With increasing temperature at a constant effective normal stress, the coefficient of friction of brucite decreases to a minimum of μ ≈ 0.20 near 300°C, and μ ≈ 0.22–0.24 in the temperature range 350–450°C. Brucite has a sheeted crystal structure, and its low frictional strength may be attributed to the relatively weak bonds between the layers. In addition, the temperature dependence of μ to ≈300°C can be explained in terms of the anomalously large coefficient of thermal expansion of brucite, which will further weaken the interlayer bonds. Brucite is a common constituent of serpentinite, and at ≈300°C, where brucite is weakest, all the major serpentine minerals have μ ≥ 0.5. The maximum expected brucite content of a serpentinite is close to 20% by weight or volume. That amount of disseminated brucite will lower the coefficient of friction of serpentinite by ≤10–15% in the deeper parts of the seismogenic zone. However, the effect will be much greater if shear can be concentrated along brucite-lined slip surfaces in the serpentinite body.
Publication type Report
Publication Subtype USGS Numbered Series
Title How brucite may affect the frictional properties of serpentinite
Series title Open-File Report
Series number 2001-320
DOI 10.3133/ofr01320
Year Published 2001
Language English
Publisher U.S. Geological Survey
Contributing office(s) Earthquake Science Center
Description Report: 14 p.; Report: Accessible (tagged) PDF file, 14 p.
Additional Online Files (Y/N) Y
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