Thermal diffusivity of some crystalline rocks
Thermal diffusivity data at room temperature and uniaxial pressure of 1 MPa are reported for five sets of crystalline rocks - granite, granodiorite, gabbro, basalt and gneiss. Diffusivity ranges between approximately 0.6 and 1.9 mm/sup 2//s, the lower end of the range being appropriate for basic rocks and the upper end for quartz-bearing acidic rocks. The scatter in diffusivity for each data set is significantly more than that of thermal conductivity, because the diffusivity of water is typically less than 10% of the diffusivity of most common minerals, whereas water conductivity is 25 - 30% of the conductivity of the minerals. For a sample set of uniform mineralogy in which porosity varies, a greater variation of diffusivity than of conductivity is therefore expected. For three of the sets sufficient mineralogical data were available to permit the assessment of methods of estimating thermal diffusivity from mineral content. All models tested yielded higher mean values of diffusivity than the means of the measured values. No model was found to be able to predict diffusivity to better than approximately 20%, but if that accuracy is sufficient, a simple geometrical model, for which only quartz content must be known, is adequate. The diffusivity data have been combined with measurements of thermal conductivity and density to provide estimates of specific heat. These all tend to be higher than those reported in the literature. For some rocks, such as the basalts, this can be explained in terms of relatively high water content and the very high specific heat of water compared with that of most common minerals. For the granites and granodiorites, the new specific heat data redefine the previously published means and ranges, by increasing the data base by approximately an order of magnitude.
- Research Organization:
- Lithosphere and Canadian Shield Div., Geological Survey of Canada, 1 Observatory Crescent, Ottawa, Ontario K1A 0Y3
- OSTI ID:
- 6103366
- Journal Information:
- Geothermics; (United States), Vol. 16:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BASALT
THERMAL DIFFUSIVITY
GABBROS
GNEISSES
GRANITES
GRANODIORITES
ACCURACY
DENSITY
GEOMETRY
MATHEMATICAL MODELS
MINERALOGY
POROSITY
QUARTZ
SPECIFIC HEAT
THERMAL CONDUCTIVITY
WATER
CHALCOGENIDES
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
MATHEMATICS
METAMORPHIC ROCKS
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PLUTONIC ROCKS
ROCKS
SILICON COMPOUNDS
SILICON OXIDES
THERMODYNAMIC PROPERTIES
VOLCANIC ROCKS
152002* - Geothermal Data & Theory- Properties of Minerals & Rocks