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Re: Tying up some loose ends.

	A few people on this list have asked me questions, and I 
have yet not responded. Today, I will do my best to answer these 
questions, as I will be out of town for three weeks, as of tommorow. 
These are questions that the entire list may be interested in reading the 
answer.
	I recieved a question a while back, about vesicles, and vugs in 
chondrules. Bascily the gentleman wanted to know why I said " By 
definition chondrules cannot have vugs/vesicles". Here now is my 
expalnation, and I apologize to the person for the delay.
	My answer is derived from an article written for a book written 
in 1983 entitled "Chondrules and Their Origins"(published by the Lunar 
and Planetary Institiute, edited by Elbert A. King). Basicly the 
definition of chondrule as of 1983, and 1988(a paper published by John 
Wasson), is an object that has been melted, and cooled rapidly, thus 
creating small and fine grained aggregates, and in some cases quenched 
glass. These are spherical to subspherical, and may contain lithic fragments.
	Now, anytime silicate material is cooled rapidly, the crystals 
tend to be small, as well as the possible formation of "volcanic glass". 
The mode of formation of chondrules precludes vesicles/vugs based on 
this, as most gas was probobly removed due to volitization when the 
material was initialy heated, thereby not allowing to be incorporated in 
to the rapidly cooling silicates. 
	Here on Earth, I am currently unaware of any igneous bodies, that 
have been cooled rapidly(i.e. obsidian deposits) that contain any 
appreciable gas bubbles. Pumice is in a sense volcanic glass that has 
cooled rapidly, and contains gas in it, but in having this property, it 
has little structural rigidity, and breaks down readily in relativly 
short geologic time. So based on the above information, it seems that 
that chondrules with vesicle/vugs are not likely to occur. However, I am 
aware that there are still many debates on what exactly a chondrule is, 
and how to define them. I choose the above definiton, because I am not a 
chondrule expert, and prefer to follow what seems plausible as realistic 
classification. I am positive, either right now, or sometime soon the 
above idea may change, but I will use the above definition until I see 
otherwise.
	One more quick comment. I have to upgrade my reference above, as 
it is somewhat incomplete. The references I need have been checked out of 
the Library here, and I can't properly site until they come back. I will 
post the reference, with page numbers when I get back.
	I had a question on the E-chondrite Earth. I will attempt to 
explain this paper in as much detail I can(M. Javoy, "The integral 
enstatite chondrite model of the earth" Geophysical Research Letters, 
Vol. 22, No. 16, Pages 2219-2222, August 15, 1995.) It should be kept in 
mind that this is an alternative to the conventional earth model that says 
ordinary chondritic material is what the earth formed from.
	The basic idea of the article is that E-chondrites match the 
earth in stable isotope, and redox characteristics. Redox is term used 
to denote a chemical reaction adding or taking away oxygen. By looking at 
these properties, models can be made to explain the differentiation of 
the earths mantle, meaning why the elements are found the way they are in 
the mantle.
	The mantle is thought to be homogeneous based on elements found in 
E,C, and Ordinary chondrites. Using simple chemistry, the depth at which 
different elements would be found in the mantle is used to try and make a 
picture of the mantle's makeup. The author of this paper 
indicates this may be wrong, and the mantle is heterogoneous. The author 
attempts to explain this by using e-chondrites as building blocks of 
planet earth.
	EH- chondrites are the material that is used in the modeling, 
because it appears to have the closest elemental, and isotopic 
compositions of the earth. The author explains in some detail the various 
effects of EH material in the earth, to show it to be feasible. The main 
point to remember is that the mantle may not be as homgeneous as 
previously thought, and that it may in fact hold two very different 
elemental compositions. I should state that no one has sampled the mantle 
directly, and there is alot of room for interpritation. 
	Basicly this model helps to explain how metal migrated to the 
core of the earth, and the compositional differences that are in the 
mantle(this is based upon thermodynamic equations,and theory, and little 
on actual specimen anaylisis). Also it gives a more rational explanation 
for oxidize Fe. Instead of trying to use "ad-hoc" change in the type of 
material being accumulated to explain this, the Fe in EH-chondrites are 
close to this state, therefore the process is much simpler to explain, and 
therfore better. 
	I hope this enlighten a few of you. I could explain the article 
in much greater detail, but that would require more writing, more than 
most would like to do in this format. Please, if you have any questions, 
let me know, and I will answer them when I get back. 

Frank Stroik
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