predict modal abundances and compositions of the major mineral phases, along ... free energy on the formation of these phases. As a first approximation, we have, ...... Si-C-O-H: Applications to metamor- phosed banded iron formations and.
THEORETICAL
PREDICTIONS
OF
•
IN
VOLATILE
SOME
BEARING
PHASES
CARBONACEOUS
AND
VOLATILE
RESOURCES
CHONDRITES
=ibamitraanguly Department
of
-TJ-
Geosciences
__y
5 5
Oniversity ofArizona Tucson AZ "
"1
.
/
Department Surendra College,
";
/
Brooklyn
Geology K.of Saxena Brooklyn, abundances which
Carbonaceous believed near-Earth Diemos, fuels
to
the
chondrites
are may
potential be exploited
missions. the nature
major
phases,
form
400
compositions. kilogram composition yields
in
C1
bearing
of
and
vapor
and
C2
1
Simulated C2 chondrite between 400 135
gm
species
temperature, becomes 550°C.
and these
heating at 2ixed 800_C at
the In
about 306 condition, of 60 kinetic librium cares
change
gm of which
of a bulk I bar
which CH4, of
as
functions
of
basis, species chondrites
volatile consist
under almost
is
CO 2 and these
molar
H2 above yield
the same completely
wt%
H20 and 40 wt% CO 2. Preliminary considerations suggest that equidehydration of hydrous phyllosilishould be attainable within a few
hours at framework
600°C. for
volatile and of carbonaceous
These further
results provide analyses of
economic resource chondrites.
the the
potentials
Introduction
The near-Earth resources of
used as purposes emphasized asteroids
also
potential asteroids detailed planetary
are which
potencan be
life supporting missions.
many of and Moon.
shown
that
three-year period, and 90,000 launch tively kilometer asteroidal launch
asteroids volatiles
Lewis and Lewis (I), at times the nearest
to Earth, and between Earth
bodies windows.
them These
within
any
can
As
these bodies
compared to These facts
volatile
resources
important analyses for missions.
nature (2,3). tion band hydrous
extraction
of knowledge
volatiles of
39 and
lunar the
make
the for future
energy-efficient from
the
the
nature
are
of
directly
problem
of most
are and
what C2
are (or
(HRTEM). recently
the small
volatile (100
The to carry predict
a
framework
which are bonaceous
bearipg 1000 A)
(CI) the
phases (5) to microhigh micro-
and McSween summary of
(5) vola-
in
the
of this work calculations and compositions
is to
mineral phases, along with and composition of the cophase, that could develop compositions of CI and C2 functions The results for
the extraction asteroids as the two small
(1,4). meteorites
identified
primary objective out theoretical modal abundances
as
examine
under optical observed under electron
phases chondrites.
of the major the abundance existing vapor in the bulk
to
An reso-
as C1 or However,
to
Zolensky presented
tile bearing carbonacous
presence of precise
chondrites of these
permit identification scope, and are best resolution transmission scopy have
minerals absorp-
and density charactersuggest that a significant near-Earth asteroids are
commonly known CM) classes.
of too
of the
materials.
carbonaceous volatile rich
grain size are often
is
asteroidal
The spectral istics strongly fraction of the made The
several
were equivocal. approach to the
the
the
more
in struc-
has been spectroscopy characterize
near 3 um suggesting phyllosilicates,
characterizations obvious alternative
the
minerals
components
of
pressure and would provide
engineering
designs
for
of volatile components from well as Phobos and Deimos, natural satellites of Mars,
also likely chondrites
to (I).
Theoretical
be
made
of
car-
Method
arbitrary
candidates supporting
or
constituent
of the volatile bearing While these studies report
Principles According classical librium system
asteroids
ly one
and
of
modal
to
Duhem's
thermodynamics state of of fixed
completely are fixed intensive, both.
Cost-effective
require
Z5
bound. There on reflectance asteroids to
pass authors
there are roughly 300 opportunities to respecand 100-meter sized as
turally studies near-Earth
the
volatile
chondrites temperature.
propellants and for planetary by are
of
the
lution
and that major
are stable chondritic
volatile,
and on a most dominant contrast, Cl
that
carbonaceous
primarily of _, H20, The relative--abundances
volatile
other
pressure suggest are the
and
of
have of
phase,
type
phases bar in
of and
work we abundances
functions of The results ± magnesite
_earing C at
about
made CO.
usually
resources of for future
this and
the
chondrites as temperature. talc, antigorite volatile below
In
volatile including
should
are
be the primary constituents asteroids and Phobos
and which
planetary calculated
have
1-
9
I
Abstract
tial
-N 11280
NY
a closed composition
determineO regardless extensive,
Ganguly
and
equilibrium
the
system and
in equi-
(i.e., mass)
a is
if any two variables of whether these are or a combination of Saxena
reviewed the various may carry out the the
theorem (6,7),
(7)
have
methods actual assemblages.
recent-
by which computation The
E-2
Table i Bulk chemical compositions of Cl and C2 carbonaceouschondrites CI Si Ti AI Cr Fe Mn Mg Ca Na K
method
C2
10.40 0.04 0.84 0.23 18.67 0.17 9.60 1.01 0.55 0.05
used
positions
12.96 0.06 1.17 0.29 21.56 0.16 11.72 1.32 0.42
0.14
Ni
1.03
1.25
Co S H
0.05 5.92 2.08
0.06 3.38 1.42
C
3.61
2.30
equilib-
sources
the (7).
of
of the naceous the
of the Lagrangian the
extremely
phyllosilicates chondrites,
effects
of
formation
of
librium
small
grain
observed one should
surface these
approximation, this effect.
free
we have, Therefore,
temperatures
of
size
in carboconsider
energy
phases.
could be lower calculations.
Table of
of
members
of
hydrous
Anhydrous
in
thermochemical
parentheses.
the
Silicates
Cl
on
As
a
the
first
however, the actual
ignored equi-
volatile
bearing
than
the
lleat
phyllosilicates
and
Data
shows C2
compositions number of
those
predicted
the
are fragments
are of
this shown
Formation
are
derived
by
reference
of
the
in
this
(Mg,Fe)SiO
Periclase
(Mg,Fe)O
(23)
Ouartz
SiO
2
(17)
Cristobalite
SiO
2
(17)
Hematite
Fe203
(23)
Magnetite
Fe304
(23)
4
work.
(8)
3
(8)
Phases
Anthophyllite
(Mg,Fe)7Si8022(OH)
Talc
(Mg,Fe)3Si4OI0(OH)
Antigorite
(Mg,Fe)48Si34085(OH)62
Chrysotile
(Mg,Fe)3Si205(OH)
Brucite
(Mg,Fe)(OH)
Magnesite
(Mg,Fe)CO and
Fe-end
Oxides (Mg,Fe)2SiO
2
(8,27) (8) (8)
4
(8)
2
(17,24)
3
(17,25)
Elements
Troilite
FeS
Pyrite
FeS
Iron
Fe
(26)
Sulfur
S
(17)
Graphite
C
(17)
C-O-H-S
(15,16,17)
Phase
H20,
CO2,
CH4,
(17) 2
CO,
(17)
02 ,
H2S,
S 2,
SO 2,
COS
compositions chondrites.
based of
work
Orthopyroxene
Carbonate
bulk
carbonaceous
Olivine
and
Base
system in
data The
I
and
These of a
Phases
and
Phases
considered
within
Species:
com-
system through multipliers
masses of
hases y our
2
numbers
Vapor
the
mental method
41.74
Table
Sulfides
the
of
the at is ele-
Because
Mg-Fe-Si-C-H-O-S
Hydrous
obtains
0.13
45.61
The
study
by minimizing of the system The minimization the various
System,
O
this
abundances
rium phase assemblages Gibbs Free Energy (G) fixed P-T conditions. constrained to conserve
0.06
P
in and
on analyses Orgueil and
E-3
Murchison meteorites, are
summarized
easily system
in
respectively,
Dodd
(22).
seen from this Mg-Fe-Si-C-H-O-S
tutes
almost
96%
compositions
of
table that (MFCHOS)
by Cl
of
C2
chondrites.
and
but
evidently
compositions system these
form
cannot chondrites.
Table we
2
have
lizing along
data. been
of
the
data the for
whose MFCHOS The
system analysis with
of
those
in
tent
with
in
the
heat of
of
the
recent
and
There
these
phases
Mg-end
of 2.
(8) the
(phlogopite yield an
and enthalpy
per K.
mole We
mate elements cafes data are
the at
values from
which
is
of
annite, difference
to and
also
by
Hemingway members
at
1 to
Mg-end members. (KJ/mol of
of the elements
free (AG_)
at 1 KJ/mol
The Fe).
bar, esti-
results Fe-talc:
-1127.53 and The corresponding energy of for Fe-talc
bar, of
2%_ Fe _-,
K
chemical of the follows.
validity
of
properties phyllosilicates The Fe-end
the
Fe-
formation and Fe-
are -4477.18 respectively.
of
estimated
the may members
of
Fe-talc
considering of the phases.
the
cations to
(TO)
layer
KJ, the
and
Fe-
relative
environments in
those
greenalite Their KJ -4577.78
in
biotite talc,
silicate
of
are
both
quite
being
and
partly which is
(28).
Thus,
2:1
similar an t:l these
phyllosilicates should have similar differences between the enthalpies of formation of the Feand Mg-end members. Further, since on the basis of observadata,
the
mineral
predicted
phases
are of
in
expected errors
compositions
of
carbonaceous to
in
be the
chon-
Mg-rich, Fe-end
the member
properties and solid solube relatively small. This understood by considering curve of a stable solution
evaluating
above
the
properties
effects
near
of
errors
Mg-terminal
of
The _ermodynamic the Feand Mg-end
of
the
anhydrous
in
segment.
thermo-
Fe-end members be tested as of talc and
mixing member
silicates
self-consistent while those assumed to be
properties components
are
taken
is
found
ideally (7). phyllosilicates solution dissimilarly
to
At
behave
behavior, but to significantly
to
be
an As
approximately the ideal
perhaps not too affect their Magnesite
ideal emphasized
of
likely 600 °c, solid
lower temperature, may deviate from
stabilities.
assumed components.
from
summary of Chatterjee of the phyllosilicates ideal for the lack
any data. The latter assumption is to be approximately valid at T > since at these conditions biotit-e
solution by
is of Ganguly
Saxena (7), the computed dehydration ditions are not very sensitive to in activity-composition relations
also Fe-Mg and
conerrors since
the devolatilization equilibria are acterized by large enthalpy changes. iron oxides and sulfides are considered
charThe to
be
solid
stoichiometric
solutions at the
and The
estimating by these the have
phases
of Mg temperatures
The Saxena (17).
The
and data.
stereochemical
relative
respectively) of -359.566
cation values
values
solution a
derived
Robie 2_nd and Fe -end
Fe-antigorite: -1094.87.
antigorite and -4784.0
for
Fe-
minnesotite equilibrium
(TOT) layer silicates, to those in antigorite,
the (8), are
enthalpies of formation from of Fe-end members of phyllosili1 bar, 298 K from the available
for the as follows
-1606.80; chrysotile:
data
data
divalent used these
publi-
phyllosilicates enthalpies
of
to
Fe-antigorite. recently deter-
oAG_ _ (minnesotite) = AGf (greenalite) = -4799.50 in the right direction from
and
com-
of
. 6712) of
compared
for have
by
according
biotite,
and Mg-
of have
number
the The
The
Chatterjee (I0) for
KJ 298
a
Fe48Si32080(OH)64
thermochemical tion model will can be easily the form of G-X
of
analogous
properties
phyllosilicate.
among
are estimated of the properties
estimated
relative of
Mg
thermochemical
are
members
and
as
results, and differ
drites effects
data
Fe27Si36086(OH)26
AG_ phase
the
consis-
comhas a
mined from
tional
(C D) and entroif _not available
in
no
members Table
known
Fe
structurally
are
also
systematizations
as discussed (13,14).
the Fe-end listed in
the
of
data set, summation
oxides
pounds, cations
are
of
the
analogous which
that of Fe27Si36090(OH)I8 for greenalite with a stoichiom-
Fe48Si34085(2_) Anovitz et
similar
unlike
experimental
capacities the phases,
self-consistent stoichiometric of
data
P-T
etry
The
chon-
However,
to and
Instead,
are closely minnesotite, of
compared Fe-talc,
divalent
phase equilibdata are similar
(9).
unstable.
phases namely,
antigorite, stabilities
phases reports
carbonaceous
are
stable pounds,
corresponding
subsystem thermochem-
of these published
distribution silicates.
any
that
crystal-
Mg-Si-O-H is based on of Chatterjee (8,11) both calorimetric and
Berman
high
Th_ (S V)
pies
of
phases
above the
determined These
Berman,
involving coexisting
the of
of
experimentally rium measurements. those
sub-
compositions lie within the (e.g., Zolensky and McSween selection of thermochemical
in the critical consistency
to
of
possible
choice by the
mineralogy
drites system (5)).
list
as
The guided
whose
constituents
the
within sources
In
this
antigorite
stoichiometry
bulk
phases of
major
shows
phases with the
ical have
the
considered
the
the computaconfined the G to this sub-
outside
be
and be
can
the subconsti-
weight
order to somewhat simplify tional problem, we have minimization calculation system,
It
sulfur assumed
fluid Fei
are
since
properties (15,16)
are and
"corresponding P-V-T authors,
For H2S
few
behave
percent
taken Robie et
state
relation, is extended
species. that
the
around a of interest.
from al.
method" as
mixing as
of
discussed to include data, H20,
we S2
as
E-4 8.00
Olivine
Antigorite
C
6.00
A
0
Fe304
2.00
0Px FeS
Talc
_hite 0.00 673
773
873
973
Temperature
1073
(K)
5.00
4.00 Antigorite
Olivine
B
\
_ 3.00 0
OPx
2.00
FeS
1.00
Talc Graphite
0.00 673
723
773
823
873
Temperature Fig.
i
rock
in
as are
Calculated (a)
C1
functions shown
modal and
of by
(b)
abundances C2
temperature
of
carbonaceous at
2
923
minerals
per
chondritic
Kb.
The
and
used the parameters
steps
in
tion tile present we do
bar,
the
calculations bearing phase not
state of believe
higher lated
free do at
the
of
compositions
the
calculations
are reliable at lower deed, we find results tures which do not systematics
Results
1
kilogram
bulk
symbols.
02 , and SO 2 and COS as CO 2, equivalent binary interaction from Saxena and Fei (15).
At
973
(K)
not T
energy >
yiel_ 400vC.
minimiza-
a
any
bearing tures.
volaAt the
thermochemical data, that our calculations
the
results
temperatures. the equilibrium
pressure
recognition phases.
of
temperatures. Inat lower temperaseem to follow the
of phases This of Some
2
Kb
so
appear procedure the of
obtained
Thus, phase
major these
we have assemblages
that at at
the
at
volatile
higher least
temperapermits
volatile phases
at calcu-
bearing may.
be
re-
S-5
P -
2 kb
C2 Cl
0.50
0.40 Olivine h
\\
V
.-
_ .....
....
x 0.30
.......
0.20
oHte
o.lo4oo' ......... 5oo' ......... 6oo' .......... 66" Temperature Fig.
placed
by
Calculated
2
C2
compositions
carbonaceous
more
chondrites
stable
assemblages
temperature, but should heating experiment. The are illustrated in Figure primary and
volatile
C2
bulk
bearing
gorite i _agnesite. around 650-C at 2 orthopyroxene (OPx) according
to
Tc
+
phases
lower
the
talc,
CI
anti-
Talc is stable and dehydrates higher temperature
=
50Px
+
Ii20.
chondrite
is
invariably
Anti-
associated
pyrrhotite (Fei_xS) (5). decomposition of troilite tire and sulfur.
Figure the
2
ferromagnesian
temperature compositions.
at
yield similar compositions bonaceous
One ratio
seems to bonaceous very
the phases
is
by
vary to
The in
the of
phase could compositions
into
an
silicates equilibration lead of
to the
in
aqueous
of the carfractionates phase
relavarying aqueous
of
phases
cares.
tant ment
contributing of variable
but
is
The
in
as It
volatile
in
kilogram are illus-
3a and abundances,
3b
of temperature noted that the
of
The change in species above
Above molar
chon-
volatiles do not change means that under equiC2 chondritic material
wil_ completely devolatize 400 C. The total yield about 14% of the initial
homogeneous phase. highest
the
impor-
species per
Figures and mass
functions should be
mas_ of the 400 C, which condition
be
an
the developof the ferro-
the solids C2 chondrites
Figure 3. the molar
not be
carbonaceous
of
with mass of
respectively, at I bar.
may to
factor in Fe/Mg ratio
abundances
trated in illustrate
and Kb.
likely
silicates
equilibrium of total
2
alteration
reason,
magnesian drites.
Cl
at
Aqueous
sole
total above librium
in
temperature
if heated above the volatile is mass of C2 chon-
th_ 400
C
abundance is due
reactioonS within 550 C, hydrogen concentration in
the has the
of to fluid the vapor
phase. Hydrogen is a very good propellant and reducing agent which may thus be preferentially chondritic
extracted material
by hea_ng T > 550 C.
to
the
C2
Fe/Mg
which
Thus, with an
a spectrum fe_romagnesian
of
In
diverse
alteration
(18).
of bulk also
observed the car-
this
silicate
drites. various
of
function
widely
achieve
aqueous
suggests pyrrho-
to
Cl and C2 at 1 bar
be a characteris%_c chondrites. Fe--
strongly
tive to degrees
as
compositions. of these phases
way
with
compositions
2 Kb for the Calculations
chondrites
ratio. Fe/Mg
shows
This (FeS)
the
to to
gor_te and magnesite crystallize at T < 550 C, but magnesite i_ absent in C2 bulk composition at T > 400 C. FeS is a stable phase at all temperatures investigated in this work. We, however, did not consider the formation of sulfate or pyrrhotite. Magnetite becomes a stable phase at T < 500°C. Elemental sulfur found in C1
....... l'obo
(C)
functions
during which that the in
are
Kb, at
Ol
at
reappear results, l, show
compositions
of as
.......
Fe/Mg sili-
contrast
to
the
C2
vol_tiles given off by 400 C consist essentially at I bar pressure. Per rial, 306
the grams The
considerable
total of
yield
which
above
of
nearly results
uncertainties
chondrites,
C1
material of H20 kilogram volatile 60 are
the
above and CO 2 of mateis
wt%
is
about H20.
subject owing
to to
the
E-6 10.0 -
A
8.0
_._ 6.0 H2 H20
O F
-_-
4.0
2.0
I CH¢ 0.0
4o'o ........'.........'.........'........8o"'o 500 600 700 Temperature (C)
150.0 Total Volatiles
B
100.0 C_ H20
50.0
CH4 X
CO_.__
0.0 400
500
600
700
Temperature Fig. the
3 Calculated volatile species
approximate
nature
properties solutions, the
effects
formation tals. any
of and of
of Further,
given
the
free
extremely fine carbonaceous
type
conditions
do
not
energy
on
grained chondrites
have
different
the
crysof
repreformed at parts
upper
ing It
o£
(Galley,
the pets.
The
volatile
bear-
abundance. that recent
studies of carto corroborate
above
abundant
as hydrous
to
the
phases
comm.). of
Devolatilization
equilibrium abov_
the
seem
made most
of
average note
to
spectroscopic chondrites
Kinetics
sented
of their
predictions
of
the solar system. However, these calculations are still useful in providing an idea of the relative stabilities, as well
stabilities
reflectance bonaceous the
mass abundances material.
phases and is interesting
nature
homogeneous
instead probably of materials at
solid ignored
(C)
molar and (b) C2 chondritic
as
thermochemical
phyllosilicate since we have
surface
compositions, but sent agglomeration different
of
the also
(a) of
equilibrium per kilogram
800
provide
calculations a
f_amework
prefor
the
E-7
7Talc
--3Anth
+
4Qz
+
4H20
P-
1
kb
6 hr=
12 hrs
120 0.0
790
800
1:
140
.lo
,=o
Temperature Fig. ature
4 and
Dehydration extent
dehydration talc remaining shown
by
of of
boundary after
asterisks,
talc as overstepping
at 1 Kb. reaction. are
from
|_
,30
,4o
(C) functions above
of time, temperthe equilibrium
Volume fraction Experimental
is data
that of points,
{19).
Greenwood
evaluation
of
the
volatile
as
well
as
some
mineralogical resource potential of Cl and C2 carbonaceous chondrites. The actual extraction of volatiles as a function of
20
temperature and heating rate, however, depends on the kinetics of the devolatilization process. For kinetic analysis, it is essential to identify the minerals in which the volatiles are most likely to be structurally bound. The above results suggest that talc, antigorite and magnesite are likely to be the major volatile bearing phases in carbonaceous chondrites.
1|
16
14
I
J= .1¢
÷
Except for pure Mg-talc, there kinetic data for the other volatile
lO
w et
;0
ing talc
8
phases. The was determined
are no bear-
dehydration kinetics by Greenwood (19).
o_ At
a given temperature, the rate o_ reaction depends on the rate constant, K , and the extent of departure from the equilibrium boundary. This is expressed in transition
6
_oo
200
aoo
400
soo
Temperature
Fig. 5 antigorite minerals Reproduced
600
700
aoo
goo
(C)
Equilibrium relations of talc, and brucite along with other in the system MgO-SiO2-1120. from
Evans
and
Guggenheim
(21).
state theory _20) according to the relation Rate = K (l-exp(n&G/RT)), where n is a constant, commonly assumed to be unity, and ^G is the Gibbs free energy of the reaction at the P,T condition of interest. Figure 4, which is constructed from Greenwood's experimental data, illustrates the dehydration kinetics of talc as functions of time, temperature and extent of overstepping (&T) above the equilibrium dehydration boundary at 1Kb. It is evident from this figure that essentially complete dehydration of talc can be achieved within
E-8 6
hours
rium
at
about
The
stability
end members interest in the 5,
160°C
above
the
equilib-
the
pure
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