Journal of Non-Crystalhne Sohds 67 (1984) 637-648
North-Holland, Amsterdam
637
A COMPARISON
BETWEEN TERRESTRIAL
IMPACT GLASSES
LUNAR VOLCANIC GLASSES: THE CASE OF FLUORINE
C. K O E B E R L ,
W . K I E S L , F. K L U G E R
AND
and H.H. WEINKE
lnstttute for Analytwal Chemtstry, Dept of Cosmochemtstry, Umoerstty of Vwnna, Austria
The genetic relattonshtp between tektites (and several other terrestrial impact glasses) and lunar
volcamc glasses has long been a point of discussion With the aid of new fluonne data we try to
furnish new evidence for the view that tektites are distract from and bear no chenucal relatIonshaps
to lunar volcanic glasses. Since fluonne analyses are only rarely made for the lond of matenal m
quesUon, we discuss here our procedures of fluonne determinations with reference to methods
newly developed in our laboratory. The first method revolves ion sensitive electrode techmques,
wlule the second uses rapid instrumental neutron activation analysis (RINAA). The results of our
determinations of fluonne in tektites and other terrestrial impact glasses are presented and
discussed together with data of lunar glasses acquired from the hterature The difference between
the chermcal behawour of tektites and lunar glasses is also found m the fluonne data It is shown
that the expectauon of htgh fluonne contents of tektites as it may be inferred from well
documented lugh fluonne contents of lunar volcamc glasses as well as a possible connection
between tektites and these glasses could not be sustained with the aid of chemical data
Thermodynarmcal data, calculated for con&tions of lunar volcanoes, leads to the conclusion that
several volatile elements are abundant dunng lunar lava fountainmg and should correlate m
volcamc glasses. Tektites fail to show these correlations, as It ts pointed out with the aid of
correlation analyses. Our data leads consequently to the conclusion that there are severe chemical
differences between tekUtes and lunar volcanic glasses
1. Introduction
T h e p r o b l e m o f t h e o r i g i n o f t e k t i t e s a n d s e v e r a l t e r r e s t r i a l i m p a c t g l a s s e s is
still u n d e r d i s c u s s i o n . A s i d e f r o m p h y s i c a l a r g u m e n t s , d i s c u s s e d f o r e x a m p l e
b y O ' K e e f e [1], C h a p m a n [2], C h a p m a n a n d G a u l t [3], C h a p m a n et al. [4],
C h a p m a n a n d L a r s o n [5], O ' K e e f e [6], F l e i s c h e r e t al. [7], D a v i d [8], O ' K e e f e
[9] a n d O ' K e e f e e t al. [10], f e a t u r i n g m a i n l y b a l l i s t i c a n d a e r o d y n a m i c a r g u m e n t s , w e w o u l d like t o p u t e m p h a s i s o n c h e m i c a l a r g u m e n t s w i t h s p e c i a l
r e f e r e n c e t o v o l a t i l e e l e m e n t c h e m i s t r y a n d e s p e c i a l l y f l u o r i n e d a t a . S i n c e it is
stated by some of the authors mentioned above that tektites resemble lunar
v o l c a n i c g l a s s e s i n t h e i r p h y s i c a l p r o p e r t i e s it m a y b e p r o m i s i n g t o l o o k f o r
chemical arguments either in favour of this interpretation or opposing a lunar
volcanic origin.
A p o s s i b l e k e y t o t h i s p r o b l e m is a n e x t e n s i v e d i s c u s s i o n o f v o l a t i l e e l e m e n t
c o n t e n t s , b e c a u s e s e v e r a l v o l a t i l e e l e m e n t s a r e g e n e r a l l y r e g a r d e d as f i n g e r p r i n t s
0022-3093/84/$03.00 © Elsevaer Science Pubhshers B.V
(North-Holland Physics Pubhshmg DlWSlOn)
638
C Koeberl et a l /
Terrestrtal trapact glasses and lunar oolcanw glasses
of volcanic processes. Some of the lighter elements (for example some of the
elements in the second period of the periodic system) seem to be of foremost
importance in this discussion. One of the most characteristic volcamc elements
is fluorine. Studies of terrestrial and lunar volcanic processes show that this
element is significantly abundant in the associated materials. Although rarely
determined it is possible to find fluorine contents for e.g. green and orange
glasses in the literature. The absence of similar data for tektites and terrestrial
impact glasses prompted us to undertake an intense investigation on fluorine
in these materials. The analytical methods used are engaging fluorine sensitive
electrodes (and wet chemical handling and extensive calibration procedures)
and rapid instrumental neutron activation analysis (RINAA) and are described
together with the results in the next section. Data for lunar volcanic glasses
were taken from the literature and are used in section 3 together with our own
tektite and impactite data m the discussion of the similarities and dissimilarities between the different materials.
2. Analytical methods
2.1. 1on sensttwe electrode techmque
Usually the analytical error has been a dominating factor in fluorine
abundance determinations m geological materials with any method, a problem
which is unfortunately very common with most light elements. Methods for the
determination of fluorine in these materials involving colorimetric methods
[11], neutron activation analysis using 19F(n, a)16N reactions [12], photon
acuvation analysis involving 19F('y, n)18F reactions [13-15] and emission spectrography [16] have been discussed, but only w~th the improvement of the ion
sensitive electrode technique (see e.g. Ingram [17]) it was possible to lower the
analytical error sigmficantly. This method has been used to some extent wltlun
lunar work by e.g. Wanke and collaborators [18].
In our laboratory an improved treatment of the fusing and solution procedures was developed some years ago by Kluger et al. [19] for use in the analysis
of terrestrial volcanic material and has been modified recently for an improved
treatment of cosmic samples as mentioned by Koeberl et al. [20]. The procedure used for the investigations discussed in this paper is as follows:
The well powdered sample (less than 250 mg) is put into a nickel crucible
(capacity about 60 ml) and about 3 g of solid N a O H is added. The fusion takes
place in a preheated furnace thermostabilized to (570 + 20)°C and is completed after 45 min. After cooling 25 ml 1 M citric acid solution is added and
about one day is allowed for complete dissolution. Simultaneously a blank
"sample" is treated with the same solution to check atmospheric and reagent
contarmnations. Following the dissolution the sample solutions are transferred
into plastic beakers and the p H of the aqueous solution is adjusted to
p H = 6.0 ___0.1. All samples were adjusted to the same volume.
C Koeberl et al /Terrestrtal tmpact glasses and lunar volcamc glasses
639
To the air contaminated blank solution 12 known small quantities of pure
N a F solution were added and the corresponding readings of the ion sensitive
electrode meter (type O R I O N ) consequently yield the calibration curve. To
avoid severe volume alterations only microsyrmges with 10, 25, and 50/~1 are
used. A diagram where the readings of the blank/calibration solution are
plotted against the fluorine contents shows that starting with an initially small
READINGS-CORR.
READINGS-UNCORR.
\
\
-- 100
\
\
\
,.I
0
In
v
U..
-- 10
,.X.
",,.X,
250
,
I
R E L . ELECTRODE
(MY)
1OO
I
POTENTIAL
?
F i g 1. C o n s t r u c t i o n o f the c a h b r a t i o n c u r v e for 1on sensitive e l e c t r o d e m e a s u r e m e n t s T h e b r o k e n
line gives the n o n h n e a r b e h a v l o u r o f the a c t u a l m e a s u r e m e n t s , w h i l e the solid h n e s h o w s the
h n e a r l z e d m e a s u r e m e n t s as o b t a i n e d b y iterative c a l c u l a t i o n s (see text)
640
C Koeberl et al /Terrestrtal tmpact glasses and lunar volcamc glasses
fluorine content there is a deviation from the hnear behavior (see fig. 1). In an
iterative procedure all reading were increased till a linear behavior of the data
points is achieved following the least squares fit method. The resulting difference between the measured and optimized curve is subtracted from all
sample results.
A similar behavior is experienced with the sample electrode potential
readings. The nonlinearity of the data is countered with the same procedure as
described above by adding known amounts of N a F solution and computerized
optimizing of the resulting second order curve. The final step is the calculation
of the tangent to this curve at the zero point (regarding the added N a F
quantities). The intersection of the tangent with the abscissa yields the sum of
the blank and sample contents. The improvement of the sample readings is
controlled by statistical considerations involving the determination of the
overall error f(t) which is assumed to be
f(t)=f(s)+
f(P)
tangent slope '
where f(s) is the standard deviation of the calibration curve as determined
from the sum of the squares of the deviations and f ( p ) is the deviation of the
first sample reading (without N a F addition) from the optimized sample curve,
in per cent. The method shows a reproducibihty as determined from multiple
analyses of better than 2%.
The results for a number of tektite and impactite samples are given in table
1.
2.2. Rapid instrumental neutron actwation analysts
A second method allowing the quick determination of fluorine without
destroying the samples has been developed by one of us (CK) in collaboration
with F. Grass (Vienna Nuclear Research Center - Atominstitut) see Grass et
al. [21] and Koeberl and Grass [22]. This work has been laid out for using
second- and millisecond-isotopes in the determination of a whole set of
elements, where fluorine is one of the about 10 or so elements accessible in
-
Table 1
Results for the 1on sensitive electrode measurements of fluonne as deterrmned by the method
described in the text
Sample no.
Class
F l uonne contents (ppm)
T8202
T8203
T8205
I8201
I8202
I8203
Indochunte
Thmlan&te
Austrahte
Zhamanslunite
Darwin Glass
Aouelloul Glass
45.7
22.0
36.8
66.8
29.8
25.5
C Koeberl et al / T e r r e s t r t a l tmpact glasses and lunar volcamc glasses
641
Table 2
Results for the RINAA fluorine determinations XDEV is the standard devlatton as received from
multiple deterrmnatlons
Sample no
Class
F (ppm)
XDEV (ppm)
T8202
T8205
T8203
18202
18205
lndochm~te
Austrahte
Thadandtte
Darwin Glass
Aouelloul Glass
44
35
21
31
12
17
12
0.8
0.5
05
7
6
6
9
7
cosmic material of this type with R I N A A methods (excluding the reactor
thermal pulse mode). The whole method and the results of the multielement
analysis of several cosmic samples will be described elsewhere, so that we
describe here only briefly the method of the R I N A A fluorine determination.
The instrumentation consists of a Triga Mark III research reactor and a
very fast self-built transportation-irradiation-measurement system, which was
installed at the reactor several years ago and has been constantly upgraded,
allowing now the R I N A A of geologic and cosmic samples. The fine powdered
samples are prepared in a special rabbit and are shot m the irradiation
chamber at the core of the reactor, where a preprogrammed irradiation time
follows, after which they are loaded directly into the measuring chamber (with
typical transportation times of < 15 ms). Three detectors are used simultaneously: a Ge(Li)-detector, a NaI-detector and a Cherenkov-detector (for
fl-emitters). The last one was used for the fluorine determinations discussed
here (isotope: 2°F, fl--decay, halflife 11.03 s). To avoid the registration of
radiothermoluminescence the plexiglass Cherenkov radiator is designed to
absorb weak fl-rays, so that only hard fl-emitters are able to produce Cherenkov radiation, which is counted with the aid of a RCA 6363 PM tube. The
main advantage of this system ~s the set up of ~ts electronic evaluation system,
which allows extremely high-rate operation with the help of the so-called Loss
Free Counting System in the Virtual Pulse Generator Version, which is
described in detail by Westphal [23-25], Popp [26], and Grass et al. [21]. The
whole system is computer controlled, as is the evaluation of the decay curves.
For some of the samples included in table 1 R I N A A fluorine determinations
have been made. The results are summarized in table 2. The error of the count
rates is usually less than or equal to + 20%, which means a tenfold increasement over the error of the ion sensitive electrode technique, showing the price
to be paid for a quick and non-destructive method.
3. Discussion
The data presented here are for tektites and other terrestrial impact glasses.
It is suspicious that all tektites and impactites possess rather low fluorine
642
C Koeberl et al /Terrestrtal impact glasses and lunar volcamc glasses
c o n t e n t s m the range of 1 0 - 6 0 p p m . To discuss the p r o p e r d a t a for l u n a r
volcanic glasses we have to take a short glimpse at the possible c a n d i d a t e s for
such a c o m p a r i s o n . T o d a y there are m a i n l y three large classes of l u n a r glasses
that are (for g o o d reasons) thought to be of v o l c a m c origin, n a m e l y the A p o l l o
15 e m e r a l d green glass, the A p o l l o 17 orange glass a n d the A p o l l o 17 V L T
glass. D e l a n o and Llvl [27], and, most recently, D e l a n o a n d L m d s l e y [28] have
been able to subdivide the k n o w n lunar volcanic glasses into 23 different
groups. These glasses are considered t o d a y as a very i m p o r t a n t p r o b e to the
n a t u r e of the m a r e b a s a l t source reservoirs. Chemical a n d petrological clues
lead to the conclusion that most l u n a r volcanic glasses ( a l m o s t all of whxch are
o f basaltic c o m p o s i t i o n ) were derived b y parUal melting from several chemically distinct source regions in a d e p t h of a b o u t (400 + 50) km.
O n e of the most suspicious facts concerning l u n a r volcanic glasses ~s their
e n r i c h m e n t with volatile elements, m o s t of which are k n o w n to be surface
correlated. T o d a y 24 surface correlated volatile elements are k n o w n ( D e l a n o
a n d Lindsley [28]), of which the most i m p o r t a n t are cited together with
references in table 3. To explain the high c o n t e n t of volatile elements a n d the
surface correlatxon it is necessary to assume that the m o o n m a y not be
u n i f o r m l y p o o r in volatiles as m a y be inferred from surface rocks, b u t that the
glass source regions are s o m e w h a t enriched in volatiles b y c o m p a r i s o n with
surface materials. T h e scenario n o w m the picture for the p r o d u c t i o n of the
volcanic glasses involves fire f o u n t a m i n g with q u e n c h i n g of the h q u i d d r o p l e t s
d u r i n g a short ballistic flight through the s i m u l t a n e o u s l y released v a p o r cloud
consisting of volatiles, leading to the a c c u m u l a t i o n of volatile elements in a n d
on the solidifying glasses. T h e scheme which we use in o u r discussions is
d e p i c t e d in fig. 2. One i m p o r t a n t c o m p o n e n t of the v a p o r cloud is fluorine.
T a b l e 4 gives a listing of calculated v a p o u r pressures of some i m p o r t a n t
inorganic c o m p o u n d s a n d elements, selected to represent c o m b i n a t i o n s of m o s t
a b u n d a n t volatlles f o u n d with volcanic glasses (with special e m p h a s i s on
fluorine), within a t e m p e r a t u r e range to be expected in l u n a r volcanic events. It
xs clearly evident that the v a p o r i z a t i o n of most elements which are f o u n d to be
surface enriched (like T1, Pb, A g etc.) is via h a l i d e c o m p o u n d s . This is a very
Table 3
Selection of 14 out of 24 volatile elements known to be surface correlated m green and orange
glasses
Element
Ref
Element
Ref
F
Na
S
C1
Zn
Ga
Br
I30,32,341
[35-371
[32,36,381
[32,34]
[32,35-38]
[32,37]
[34]
Ag
Cd
In
Sb
Tl
Pb
B1
[351
[35-371
[35,37]
I35]
[32,39]
[32,36,39,40]
[351
C Koeberl et al / Terrestrtal tmpact glasses and lunar volcamc glasses
~
~
:
~
~
-
~
7~.~'..7~.~,,~
~
,
ii
_~
~
~
.
;
~
~
643
. . . .
~--~-~---~.1-'.
l
•.
-~--"~-'~='~3
~ - - - ~ = - - - - ~ ~ ~ ~
" -I~-.2-~-~~~--~---~"~--
"
~
-~z~-'--~
~
F~g 2 Scheme of the model of lunar lava fountammg and volcamc glass production as dxscussed m
the text The vapour released consists mainly of the compounds d~scussed xn table 4
likely mechanism for the deployment and incorporation of large amounts of
fluorine xn and on these glasses.
The largest fluorine content ever reported for lunar material is (0.27 +
0.11)%F by weight as pubhshed by Patterson et al. [29] for an m s t t u chemical
analysis of lunar highlands material performed by the Surveyor 7 alpha
particle scattering experiment. It is believed that this high value reflects some
micron thick layers at the surface of the Surveyor 7 samples, which could be a
result of deposition of volcanic exhalations. Lunar volcanic glasses show a
similar large fluorine content, although not often as large. One of the highest
concentrations in a surface film was reported by Goldberg et al. [30] to be
about 3000 p p m for green glass obtained from a 15427 clod. They also report
large surface concentrations for 15012 fragments (about 500 ppm). Similar
fluorine enrichments have been reported not only for the surfaces but also for
the bulk of green and orange glasses from rocks 15425, 15426, 74220, 74241,
74261 and others (see e.g. refs. [31] and [32]). Thus it seems very hkely that
fluorine is a good indicator of volcamc processes not only on the earth (see e.g.
644
C Koeberl et al /Terrestrtal Impact glasses and lunar volcamc glasses
Table 4
Thermodynanucal data for several morgamc compounds and elements. The values have been
calculated from raw data and constants given m ref [41]. These compounds occur most probably
within lunar lava fountammg
Compound/
Bolhng point Vapour pressure (Torr) at different temperatures (K)
element
(K)
LIF
NaF
KF
LICI
NaCI
KC1
PbC12
AgCl
LBr
NaBr
KBr
PbBr 2
Ag
Sb
Tl
Pb
B1
1949
1968
1778
1598-1633
1686
1773subl.
1233
1823
1538
1663
1708
1189
2485
2023
1730
2013
1833
800
900
1000
1100 1200
1300
1400
4.07
0 50
2)<10 -2
5.37
8)<10 -2
0.17
3.44
0.59
1.17
1 23
6 61
0.29
1.44
0.75
1.19
2 77
4.57 18 2
14 2 47 4
2.89 12.1
413
6.13 225
686
5.32
214
3)<10 -2
155
26.3
8.21
6.41
28.5
22.6
1500 1600
14 1
41.7
33.1
58.9
18 1
83 0
668
4.00
6.68 28 7
8 26
0 72
1 48
6.93 26 0
Kluger et al. [19] and Kiesl et al. [33]) but also on the moon. If tektites should
have their origin within lunar volcanic processes we shall also expect large
fluorine contents in this material. As can easily be seen from tables 1 and 2 this
is not the case for tektites and impactites. On the contrary, they exhibit rather
low values, even when compared to terrestrial materials, i.e. when compared to
e.g. sedimentary rocks, which are thought to be the main parent material in the
case of a terrestrial impact origin of tektites. A possible explanation for this
effect will be offered below. Together with other problems, like the fact that
lunar volcanic glasses are generally of basaltic nature (tektites and impactites
are, with the exception of Lonar Crater glass, of granitic nature) and that
granitic glasses are very rare on the moon, usually occurring as pseudogranitic
interstitial glasses within basaltic matrices, consistent with a model of their
origin as crystallization products from a residual liquid remaining from an
almost totally solidified basaltic magma, this points against a genetic relationship between lunar volcanic glasses and tektites. A possible exception, however, has been noted by Glass [42], who discovered high-silica glass particles in
Apollo 14 lunar finds (14259, 20), which he subdivided in several subgroups.
While the origin of all but one of these groups is explained via mare basalt
residuals crystalhzation, Glass' group E is possibly of volcanic origin.
To perform an additional test we had a closer look at several other elements
in tektites which can be expected to be prominent during lunar lava fountaining. Some of these elements are supplied by calculations like the ones
645
c Koeberl et al / Terrestrial tmpact glasses and lunar volcamc glasses
p r e s e n t e d in t a b l e 4. T h e r e it is s h o w n t h a t f l u o r i n e a n d several o t h e r h a l i d e
c o m p o n e n t s o f s o m e v o l a t i l e e l e m e n t s will m o s t p r o b a b l y b e a b u n d a n t d u r i n g
l u n a r v o l c a n i s m , so t h a t w e m a y e x p e c t t h e m to c o r r e l a t e in these m a t e r i a l s . A
set o f s o m e o f t h e s e e l e m e n t s , w h i c h h a v e b e e n d e t e r m i n e d in the c o u r s e o f
s o m e m u l t l e l e m e n t a n a l y s i s s e q u e n c e s in o u r l a b o r a t o r y in the s a m e s a m p l e s
w h i c h are m e n t i o n e d m tables 1 a n d 2, was c h e c k e d for p o s s i b l e c o r r e l a t i o n s .
T a b l e 5 gives the a n a l y t i c a l d a t a for s e v e n e l e m e n t s b e n e a t h f l u o r i n e , w h i l e
t a b l e 6 gives the results o f t h e m a t h e m a t i c a l c o r r e l a t i o n a n a l y s i s for t h e
element pairs F/K, F/Na, F/Se, F/Sb, F/Zn, F/Rb, and F/Mg. The only
s i g n i f i c a n t c o r r e l a t i o n t h a t c o u l d b e d e t e c t e d is a c o r r e l a t i o n b e t w e e n F a n d
a n t i m o n y w i t h a c o r r e l a t i o n c o e f f i c i e n t o f 0.94. T h e d i a g r a m d e p i c t i n g this
c o r r e l a t i o n is g i v e n in fig. 3. A l l o t h e r c o r r e l a t i o n c o e f f i c i e n t s fall b e l o w a
s i g n i f i c a n c e b o r d e r . T h i s s e e m s to b e a n o t h e r a r g u m e n t a g a i n s t a n y relat i o n s h i p w i t h l u n a r v o l c a n i c glasses. I n t h a t c o n t e x t it m a y b e p r o m i s i n g to
c h e c k c r o s s c o r r e l a t i o n s b e t w e e n the h a l o g e n e l e m e n t s n o t o n l y in t e k t i t e s b u t
a l s o in g r e e n a n d o r a n g e glasses.
I n the c a s e t h a t w e m a y a c c e p t the t e r r e s t r i a l i m p a c t t h e o r y as a n o r i g i n o f
t e k t i t e s a n d i m p a c t i t e s we h a v e to e x p l a i n w h y the f l u o r i n e c o n t e n t o f t e k t i t e s
is n o t o n l y s i g n i f i c a n t l y l o w e r t h a n t h a t o f l u n a r glasses b u t also l o w e r t h a n in
Table 5
Analytical data for seven elements m addition to fluonne as detenmned dunng some multlelement
analyses m flus laboratory
Sample no F (ppm) Na20 (%) K20 (%) Se (ppb) Zn (ppm) Rb (ppm) Sb (ppm) MgO (%)
T8202
T8203
T8205
18201
18202
18203
18205
45 7
22 0
36.8
66.8
29.8
25.5
12.7
1 31
1 17
1 12
1.69
0.11
0.34
0 37
2.84
2.85
2 51
3 38
2 14
2 16
2.37
2.9
0 74
19
1.8
2.0
108
4.1
0.29
5 78
1 79
11 4
1.26
4 65
0.59
133
98
80
78.9
74.1
39.8
47
0.49
0.26
0 055
0.73
0.29
0 14
0 13
2 19
2.27
2 87
1.52
0.96
1.80
2 22
Table 6
Results for correlauon analyses for seven element parrs with fluonne Given is the correlation
coefhclent rxv and the value for F for use m the F-distribution, allowing a further check of the
significance of the correlation coefficient
Correlation
Gy
F
F/MgO
F/Rb
F/K20
F/Na20
F/Zn
F/Se
F/Sb
- 0.22
0.49
0 85
0 86
0 69
- 0.25
0.94
0 25
1 58
13.2
14.2
4.54
0 33
39.5
646
C. KoebeH et al. /Terrestrtal impact glasses and lunar volcanic glasses
0
O.I
O
¢n
B
'11
Z
0.2
•
•
O
aO
40
F
SO
( a, p M )
Fig. 3. Correlation diagram showing the element pair fluorine/antimony, the only one which
reveals a correlation within the set of element pairs investigated in table 6, The correlation
coefficient rxy is 0.94.
terrestrial parent materials like sedimentary rocks. It is proposed that some
kind of shock-release of fluorine takes place. Since it is known from glass and
mineral chemistry that the F - ion easily replaces the O H - ion without any
further alteration of the matrix a similar shock induced process is possible
within the impact altered parent material, where F may escape in the form of
some spontaneously in situ formed extremely volatile compounds like HF
(from H20).
4. Conclusions
In this paper we presented fluorine data for several tektites and impactites,
where a surprisingly low fluorine content of these materials has been revealed.
A possible connection with lunar volcanic glasses has been discussed using
models of lunar lava fountaining and volcanic glass production together with
the composition of volatile exhalaUons as derived from thermodynamic calcu-
C Koeberl et a l /
Terrestrtal tmpact glasses and lunar volcamc glasses
647
l a u o n s a n d v o l a t i l e e l e m e n t s u r f a c e e n r i c h m e n t s o n g r e e n a n d o r a n g e glasses.
The remarkable difference between the fluorine content of tektites and lunar
volcanic glasses points against a connection between these two classes of
n a t u r a l glasses. T h i s p o i n t is f u r t h e r s t r e n g h t e n e d w h e n w e c o n s i d e r c o r r e l a tions between several volatile elements which could be expected to occur in
l u n a r v o l c a n i c e x h a l a t i o n s ( a n a s s u m p t i o n w h i c h is d e r i v e d f r o m v a p o r p r e s s u r e c a l c u l a t i o n s a n d a n a l y t i c a l d a t a f r o m g r e e n a n d o r a n g e glasses). A l l b u t
o n e o f t h e c o r r e l a t i o n s i n v e s t i g a t e d h a v e p r o v e n t o b e n e g a t i v e , i.e. t h e r e a r e
n o n e . So f r o m t h e c h e m i c a l p o i n t o f view, e s p e c i a l l y w h e n c o n s i d e r i n g f l u o r i n e
as a n i n d i c a t o r o f v o l c a n i c p r o c e s s e s , t h e r e is a s i g n i f i c a n t d i f f e r e n c e b e t w e e n
lunar volcanic glasses and tektites.
W e w o u l d like t o t h a n k D r F. G r a s s f o r h e l p w i t h t h e R I N A A m e a s u r e m e n t s , a n d D r J.A. O ' K e e f e f o r v a l u a b l e c o m m e n t s o n t h e m a n u s c r i p t .
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