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INTRODUCTION

The electrical properties of a material define its behavior when an electric field is applied. The two principal electrical properties are the dielectric constant, which is a measure of the electrical polarization that takes place when an electric field is applied, and the conductivity, which is a measure of the conduction current developed by an electric field.

In accordance with modern usage, the MKS unit for conductivity, the mho per meter, is used in these tables. More commonly the reciprocal of conductivity, the resistivity, measured in ohm-meters, is used. In the case of dielectric constant, the tables are compiled in terms of the ratio:  
dielectric constant = specific capacity of material specific capacity of vacuum ˙
To obtain the specific capacity of a material from the data listed in these tables, it is necessary to multiply the values listed by the specific capacity of a vacuum, 8.85 × 10−12 farads per meter.

ELECTRICAL RESISTIVITY

Materials are classified in a general way as conductors, semiconductors or insulators. A material with a resistivity of 10−5 ohm-meters or less is classed as a conductor; materials with a resistivity greater than 108 ohm-meters are classed as insulators; materials in the intermediate range are semiconductors.

Resistivities which have been reported in the literature for individual materials are listed in Table 26-1. These data were obtained at ambient room temperatures, ranging probably between 15° and 30° C, and at a sufficiently low frequency that these may be classed as D.C. measurements.

The minerals listed in Table 26-1 are all conductors or semiconductors. They are such rarely

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