From: jgacker@news.gsfc.nasa.gov (James G. Acker)
Subject: Re: Ginenthal on Venus' Surface Phenomena
Organization: NASA Goddard Space Flight Center - Greenbelt, MD USA
X-Newsreader: TIN [version 1.1 PL6]
Date: Tue, 12 Jan 1993 15:51:47 GMT

I am really going to regret this.  The abstract that addresses
part of Ginenthal's statement is the longest and most
complex I've seen in a meeting transactions.  Sigh.

news (news@fedfil.UUCP) wrote:

: Ginenthal cites further evidence, as if any were needed from one of the
: favorite realms of several of the t.o regular crew, i.e. Chemistry.
: Given standard theory, you'd not expect a lot of iron compounds lying
: around on Venus' surface:
: 
: 
:      "As a newbom planet, Venus would  not  have  fully  differentiated
:      so  it  remains  possible  that all its iron has yet to sink
:      to its core.  Accordingly, it was reported in Astronomy that:
: 
:          Maxwell Montes ... poses a big problem in interpretation.
:          Parts  have  electrical  properties that indicate the surface
:          contains "flakes"  of  -some  unknown  mineral,  most  likcly  iron
:          sulfides, iron oxides, or magnetite.  Iron sulfides ("fool'
:          s gold") fit the observations best,  but studies havc shown
:          that they  would  be  quickly  destroyed  by  the  corrosive
:          Venusian  atmosphere.  Iron oxides  (such  as  hematite)
:          and  magnetite  are  also  possible,  but  the  a
:          presence of either is not easy to account for.
: 
:      "If indeed iron is to be found upon the surface of Venus
:      it would support  the  claim  that  it  is a youthful planet

	There's a lot of iron on Earth's surface too -- especially
if you include the sea floor.  Think about it.


:      in the early stages of cooling. A planet that had  differentiated
:      its  iron  into its central core would not be expected
:      to  pour  iron  onto  the  surface  with  volcanic  materials.

	Oh?  Ever hear of basalt?  Do a little basic mineralogy, Mr.
Ginenthal.  You too, Ted.


:      The  reason  that  the  iron  compounds   have   not
:      completely   corroded   in   Venus'   corrosive  atmosphere,
:      most  probably,  is  that  these  outpourings  of  iron
:      are  extremely  recent   surface coverings  measured  in
:      perhaps  a  few  years.  Iron  on  Venus'  surface  is
:      clear  evidence  that  supports Velikovsky.


	Ah well.  What could those mysterious minerals be?  Has this
mystery completely baffled the entire scientific community?
	Uh, not exactly.

	"Venus Surface Mineralogy:  Origin of the Altitude Dependent
Low Radiothermal Emissivity Regions"  Roger G. Burns and D'Arcy W. Straub,
Dept. of Atmos. and Planetary Sciences, MIT, Cambridge, MA  02139;
phone # on request.

	Confirmation of high-radar reflectivity regions in Venusian
mountainous volcanic terranes during the current Magellan mission have
heightened speculations about altitude-dependent mineralogical phase
changes on Venus.  The low microwave emissivity/high radar reflectivity
behavior is attributed to materials with large dielectric constants.
Thus, the high dielectric constant of pyrite measured at ambient
temperatures on Earth has engendered the widespread belief that FeS2 is
present in high-elevation surface assemblages and that "fool's gold" is
responsible for the low radiothermal emissivities of Venus.  However,
controversy centers around the thermodynamic stability of FeS2 in
atmospheric CO2 + CO relative to Fe3O4 (magnetite) plus COS (Fegley et al.,
Proc. LPSC, 22, 3-19, 1992;  Klose et al., JGR, 97, in press, 1992).

	Because the dielectric constant, e is accentuated in
a phase having an electrical conductivity, s, exceeding 0.1 omegaE-1 mE-1,
and since some mixed-valence Fe2+ - Fe3+ minerals exhibiting
electron delocalization may also possess relatively high s values
at elevated temperatures, we have assessed the stabilities of selected
Fe2+ - Fe3+ oxide and silicate minerals under temperature (T = 400-475
deg. C) and oxygen fugacities (fO2 <= 10E-21) existing on the
Venusian surface.

	Magnetite (Fe2+Fe3+)2O4, with s475 = 14000 omegaE-1 me-1, is the
best-known highly conducting mixed-valence iron mineral.  Our Mossbauer
spectral measurements of hematite heated at Venusian T - fO2 conditions
(Straub and Burns, LPS, XXIII, 1375, 1992) demonstrated the relatively
rapid conversion (100% within a month) of Fe2O3 to Fe3O4, confirming
the calculated thermodynamic stability of magnetite on Venus.  Laihunite
(Fe2+Fe3+)2Si2O8, with s475 = 1 omegaE-1 mE-1, was also suggested to
occur on Venus.  However, Mossbauer spectral measurements of a variety
of natural and synthetic ferrifayalites (derived from oxidized Mg-Fe
and Mn-Fe olivines) demonstrated that they are rapidly reduced to
Fe2+-olivines in the T-fO2 regime of Venus.  Some dehydroxylated
oxyhornblendes and oxybiotites have proven to be stable Fe2+ - Fe3+
silicate assemblages below 475 deg. C and at fO2 <= 10E-21, so that
kaersutite and oxyannite could exist on Venus, __perhaps as products
of chemical weathering__.  Indeed, the high K content of surface rocks
at the Venera 14 site (Surkov et al., JGR, 80, B393, 1984), may be
indicative of biotite.  Ilvaite, Ca2+Fe2+Fe3+ Si2O8(OH) with s475
= 400 omegaE-1 mE-1, is another viable candidate for the high-
altitude, highly-conducting mineral assemblage on Venus.  This mixed
valence Fe silicate, which forms in CO2-saturated rocks on Earth during
contact metamorphism when magma intrudes ferruginous carbonates, becomes
stable relative to calcic pyroxene and magnetite assemblages below
450 deg. C (Gustafson, J. Petrol., 15, 455, 1974).

	Some impact craters and plains areas at low elevations on Venus also
show low emissivities.  We interpret these areas to contain pentlandite-
pyrrhotite assemblages associated with impact-generated __basaltic__ flows,
by analogy with the terrestrial astrobleme at Sudbury, Ontario.  The
concept of a "loaded dielectric", based on dielectric constant measurements
of pyrite-bearing metavolcanic rocks and the sulfide ore from Sudbury, have
figure prominently in interpretations of high radar-reflectivity regions on
Venus (Pettingell et al., JGR, 93, 1488, 1988).  The Sudbury ore sample
used in earlier dielectric constant measurements (Nozette, Ph.D. diss. MIT,
1982), which ws deduced to contain 45% pyrite and 45% chalcopyrite and
accessory pyrrhotite, may have been misidentified and consisted, instead,
of pentlandite-pyrrhotite (and accessory pyrite, chalcopyrite) assemblages,
accounting for the very high conductivity and immeasurable dielectric
constant of the Sudbury ore samples.  Riffling on pyrrhotite (+ pentlandite)
from _basaltic_ magma flowing over fractured terrane may account for
some linear high radar reflectivity regions on Venus.


	Jim Acker
	jgacker@neptune.gsfc.nasa.gov









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