[meteorite-list] TROILITE VAPORIZATION IN CARANCAS

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun, 21 Oct 2007 15:19:44 -0500
Message-ID: <0f6401c8141f$b90392e0$b92ee146_at_ATARIENGINE>

Hi, List (sorry, Adam),

    After "touting" the idea that the Carancas impactor
vaporized its troilite content and created a quasi-explosive
event, I have discovered I picked up one erroneous piece
of data: 700 degrees K. is not the "vapor point" of troilite;
it is the condensation temperature of gaseous troilite in a
near vacuum, and is lower than the melting and boiling
point of troilite.

    Here's the actual data, which does not preclude a troilite
vaporization even though the data is not that simple: the
melting point of FeS is 1463 K. The total heat to raise it
from 0 K to its melting point is 88 kiloJoules per mole.
The heat of fusion is 31 kiloJoules per mole, or a total
of 119 kJ/mole to melt. Then comes boiling...

    Boiling troilite is complicated. After 94 minutes of
Googling, I discover, in a paper too complicated for me
to understand, the statement that measuring the boiling
point of troilite is too complicated to explain in this paper.
Big help.

    It varies with the compositional variety, is changed by
the other mineral phases present, yada, yada. It also
appears that hot melted troilite dissociates very rapidly.
The sulfur released from melted troilite is a vapor as
the boiling point of sulfur is very much lower than troilite;
you can boil a spoonful of sulfur with a big match. Just
try it.

    The troilite exists as nodules in the rock, which the
first Bolivian analysis gives as "ultramafic," so I looked
for forsterite. Here the corresponding physical data for
forsterite: melting point is 2171 K; total heat is 360 kJ,
and the heat of fusion is 71+/-21 kJ, or 410-452 kJ/mole
to melt it. And that's one of the easier rocks to melt and
vaporize...

    You can see that it takes vastly more energy to melt
"rock" (and vaporize it) than it does troilite, three-and-a-half
times more. This is the important fact, because an impact
is a "mechanism: to transform kinetic energy into heat. The
temperatures achieved are created entirely by the converted
energy of the impact.

    It turns out that velocity necessary to reach the kinetic
energy of 119 kJ/mole for troilite is 1644 meters per sec. Since
velocities for 2000 m/sec and up have been proposed here
on the List for a "large, slow" impactor, there seems to be
no problem with the "troilite explosion" theory. It still fits
the parameters we know (or think we do).

    And, as long as I am dining on crow: crow a la orange,
broasted crow, crow fricassee, crow burgers, crow a la
King, fillet of crow... (For readers in Europa, I suspect the
expression "eating crow" is exclusively an American slang
backwoodism; it means confessing to an error.) There is one
more error.

    I mentioned large free iron inclusions in Carancas. The
term "large" is an error. There is a photo in the Max Schreier
Planetarium Publication20070929014416208.pdf of an iron
melt that has filled the veins and hollows of Carancas, which
they interpret as meaning the original meteoroid was heavily
shocked in its earlier life (something we can agree to). But I
failed to notice the SCALE of the photo; it wasn't a big inclusion,
although there are reports of free iron inclusions (usually found
knocked free from any matrix) in the sub-centimeter range.
There could be "large" free iron inclusions, but if there are,
they haven't been found.

    If anyone (else) finds any more errors, let me know;
I still have some nicely chilled left-over crow sandwiches
in the refrigerator.


Sterling K. Webb
Received on Sun 21 Oct 2007 04:19:44 PM PDT