Alkali and Earth Alkali Elements
43
respect to quartz (from 0.6 to 2.7%0). The feldspar enrichment increased
systematically from the outer edge of the pegmatite to the inner quartz
core boundary. This finding may be explained by assuming crystal
growth from a interconnected vapor phase, with silicon isotope fractionation between solid and vapor phases.
A few measurements of sedimentary and biogenic silicon showed a
wide scatter of values throughout the observed range of natural variation.
A more complete understanding of the measurements requires additional data from natural and laboratory systems.
IX. Chlorine and Bromine
1. Chlorine
Chlorine has two stable isotopes with the following abundances
(BOYD et aI., 1955):
75.53% ,
24.47% .
Chlorine plays a key role in chemical atomic weight determinations.
Possible differences in the natural isotope ratio may have great importance in the determination of atomic weights.
Theoretically we would expect small variations in the isotopic composition of chlorine, for instance, in the late precipitations of evaporites,
analogous to sulfate-containing evaporites. HOERING and PARKER (1961),
MORTON and CATANZARO (1964), and OWEN and SCHAEFER (1955), however, reported no measurable differences in the isotopic composition of
chlorine.
2. Bromine
The two bromine isotopes, 79Br and slBr (BAINBRIDGE and NIER,
1950) have almost equal abundances:
79Br:
50.52,
slBr:
49.48.
CAMERON and LIPPERT (1955) have not found any detectable differences
in the isotopic composition of bromine.
X. Alkali and Earth Alkali Elements
The results of the relatively few and sometimes contradictory isotope
measurements of the alkali and earth alkali elements are combined in
43
respect to quartz (from 0.6 to 2.7%0). The feldspar enrichment increased
systematically from the outer edge of the pegmatite to the inner quartz
core boundary. This finding may be explained by assuming crystal
growth from a interconnected vapor phase, with silicon isotope fractionation between solid and vapor phases.
A few measurements of sedimentary and biogenic silicon showed a
wide scatter of values throughout the observed range of natural variation.
A more complete understanding of the measurements requires additional data from natural and laboratory systems.
IX. Chlorine and Bromine
1. Chlorine
Chlorine has two stable isotopes with the following abundances
(BOYD et aI., 1955):
75.53% ,
24.47% .
Chlorine plays a key role in chemical atomic weight determinations.
Possible differences in the natural isotope ratio may have great importance in the determination of atomic weights.
Theoretically we would expect small variations in the isotopic composition of chlorine, for instance, in the late precipitations of evaporites,
analogous to sulfate-containing evaporites. HOERING and PARKER (1961),
MORTON and CATANZARO (1964), and OWEN and SCHAEFER (1955), however, reported no measurable differences in the isotopic composition of
chlorine.
2. Bromine
The two bromine isotopes, 79Br and slBr (BAINBRIDGE and NIER,
1950) have almost equal abundances:
79Br:
50.52,
slBr:
49.48.
CAMERON and LIPPERT (1955) have not found any detectable differences
in the isotopic composition of bromine.
X. Alkali and Earth Alkali Elements
The results of the relatively few and sometimes contradictory isotope
measurements of the alkali and earth alkali elements are combined in