# Dictionary:Metal factor (MF)

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A measure of the total frequency-dependent change in conductivity or capacitivity of a rock, used in the interpretatation of IP data. Metal factor is the percent-frequency-effect (q.v.) normalized by dividing by the measured resistivity (ρα in ohm-feet) and multiplied by a constant:

${\displaystyle MF=2\pi 10^{3}{\frac {(PFE)}{\rho _{\alpha }}}}$

1. Originally metal factor was defined as

${\displaystyle MF=2\pi 10^{5}({\frac {\rho _{dc}-\rho _{ac}}{\rho _{ac}-\rho _{dc}}})}$

where ρdc is the low-frequency resistivity and ρac is the high-frequency resistivity in ohm-feet.

2. In the frequency domain the definition used is

${\displaystyle MF=2\pi 10^{5}{\frac {\rho _{dc}-\rho _{ac}}{\rho _{dc}\rho _{ac}}}}$

3. In the time domain, the metal factor is

${\displaystyle MF={\frac {2000M}{\rho _{dc}}}}$

where M is chargeability in millivolt-seconds per volt and ρdc is in ohm-meters. This unit is similar to Keller’s parameter, specific capacity (q.v.) or static capacity.

4. A constant times the ratio (sometimes called electric susceptibility or capacitivity) between induced-current dipole moment per unit volume (P) and electric field (E):

${\displaystyle MF={\frac {2\times 10^{6}P}{E}}}$

The metal factor has units of conductivity. It is also called metallic-conduction factor.