# Typical Values for Rocks and Other Materials¶

The range of relative permittivities for rocks and other materials is tabulated below. Also included are: the average propagation velocity ($$V_{avg}$$) of radiowave signals, the conductivity ($$\sigma$$) and the approximate penetration depth of radiowave signals; these are relevant to ground penetrating radar.

Rocks within a certain classification vary significantly in composition. As a result, particular rock types made be characterized using a range of relative permittivities. By examining the table below, several things can be inferred:

• Water has a much higher dielectric permittivity than rock forming minerals.

• Water saturated rocks have larger dielectric permittivities than dry rocks.

• Saturated sediments generally have larger dielectric permittivities than hard rocks.

• The variation in dielectric permittivity for sediments is larger than it is for hard rocks.

• The combination of conductive and dielectric properties for each material results in significant variations in penetration depth for radiowave signals.

Material

$$\varepsilon_r$$

$$V_{avg}$$ (m/ns)

$$\sigma$$ (ms/m)

Penetration Depth (m)

Air

1

3

0

$$\infty$$

Fresh Water

80

0.033

0.5

285

Sea Water

80

0.01

3000

< 0.1

Ice

3 - 4

0.16

0.01

3000

Dry Sand

3 - 5

0.15

0.01

3200

Saturated Sand

20 - 30

0.06

0.1 - 1

145

Limestone

4 - 8

0.12

0.5 - 2

30

Shales

5 - 15

0.09

1 - 100

1

Silts

5 - 30

0.07

1 - 100

1.3

Clays

5 - 40

0.06

2 - 1000

0.2

Granite

4 - 6

0.13

0.01 - 1

65

Anhydrites

3 - 4

0.13

0.01 - 1

55