848 GEOPHYSICAL WELL TESTING [Chap. U 



and rocks is in the neighborhood of 0.2 for dry rocks, but it may increase 

 to 0.5 to 0.7 for moist formations. Wet peat, with 0.9, approaches the 

 specific heat of water. Table 76 gives a few representative values, in cal. 

 gram" centigrade" . 



Table 76 



SPECIFIC HEATS 



MINERALS 



Feldspar 0.21 Calcite 0.20 



Dolomite 0.22 Quartz 0.21 



Gypsum 0.26 



SEDIMENTARY ROCKS 



Sandstone 0.22 Loam (wet) 0.51 



Slate 0.22 Sandy loam (dry) 0.49 



Clay 0.22 Sandy loam (wet) 0.75 



Quartz sand 0.19 Humus soil . 44 



Chalk 0.21 River sand (moist) 0.32 



Coal 0.31 Peat (dry) 0.15 



Loam (dry) 0.31 Peat (wet) 0.9 



IGNEOUS ROCKS 



Granite 0.19 Andesite 0.20 



Gneiss 0.20 Basalt 0.21 



Porphyry 0.20 Syenite 0.20 



Specific heat of rocks is determined by any one of the calorimetric 

 methods used for other sohds. For instance, the specimen may be heated 

 to a given temperature, and then be dropped in a calorimeter. The 

 quantity of heat given off until both specimen and bath have reached the 

 same temperature is dependent on the specific heat of the specimen. 



Compared with the metals whose conductivity, when expressed in units 

 of cal. cm.~ sec." centigrade" , may be as much as 1 unit (silver), most 

 rocks have only a conductivity of third decimal value. Most sedimentary 

 and some metamorphic rocks are distinctly anisotropic with respect to 

 heat conduction. The anisotropy ratio is about 1^:1 (gneiss) to 3:1 

 (schists). Table 77 gives heat conductivities for a few minerals and rocks 

 in 10"' C.G.S. units. 



Table 77 

 HEAT CONDUCTIVITIES 

 MINERALS 



Coal 0.3-0.8 Calcite 10 



Petroleum 0.3 Graphite 12 



Mica 0.9 Rock [salt 17« 



Water 1.4 Quartz ± 17 



Ice 2-6 Fluorite 25 



Gypsum 3 Magnetite 30 



Feldspar 5 Quartz || 32 



" This value ia for crystals and is probably too high for salt formation. Leonardon (Geophysics, 1[1I, 115, 

 [Jan., 1936]) gives 6.6, which value is also quoted by Alexanian. 



