Encyclopedia of Environmental Science and Engineering, Volume I and II

WATER: PROPERTIES, STRUCTURE, AND OCCURRENCE IN NATURE 1295

TABLE 3

Crystallographic properties of ice polymorphs

a^

Ice

I

Ic

II

III

V

VI

VII

VIII

Crystal system Space

group

b Unit cell

Hexagonal

P6/mmc

Cubic F43 m

Rhomboherdral R3

Tetragonal P4

(^21)
(^21)
Monoclinic A2/a
Tetragonal P
/nmc 2
Cubic Im3m
Cubic Im3m
dimensions (A)
c
a4.48
c7.31
a6.35
a7.78
a113.1º
a6.73
c6.83
a9.22,
b7.54
c10.35,
b109.2º
a6.27
c5.79
—
a3.41
N. molecules/unit cell
4
8
12
12
28
10
2
2
Density at

175ºC,
1 atm (g cm
^3
)
0.94
—
1.17
1.14
1.23
1.31
—
1.50
Density at (
TºC,
P
kbar) in region of
stability (gcm
^3
)
0.92 (0º, 1)
0.93 (

130º, 1) 1.18 (

35º, 2.1)
1.15 (

22º, 2.0)
1.26 (

5º, 5.3)
1.34 (15º, 8)


1.65 (25º, 25)

1.66 (

50º, 25)
a Data for ices I and Ic are from Lonsdale (1958); data for the high-pressure pol
ymorphs are from Kamb (1965
a, b
), Kamb.
b The space groups for ice VI, VII, and VIII are not entirely cer
tain.
c For 1 atm and

175ºC, except for ice Ic which refers to

130ºC.
C023_004_r03.indd 1295C023_004_r03.indd 1295 11/18/2005 11:12:32 AM11/18/2005 11:12:32 AM