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Re: Building the Solar System: A look at element classification.

	Hello to everyone on this list! I have been gone a while, so let 
me introduce myself to those new to the list. My name is Frank Stroik, 
and I am at the University of Wyoming Geological Museum, and Department of 
Geology and Geophysics. I am student/researcher, studying Geochemistry, 
and Petrology. 
	I would like to discuss what makes up meteorites, Planets, 
Asteroids, Comets, Moons, and space dust. All the above planetary bodies 
are made up of elements, as we all know, but what properties do these 
elements have, and why are they found the way they are. 
	This answer will provide insight into why Chondrites for example, are 
composed of  
primarly two minerals, Pyroxene, and Olivine, and not, say, Quartz, or 
Corundum. Also we begin to understand why elements become distributed in 
planetary bodies, and why they bond to each other in certain ways. 
	It is my hope that we will be able to start a journey that never 
ends, one that leads us closer to understanding the Solar System we 
inhabit, and the Universe it is in. I will post additions to this line of 
thought periodicaly throughout the next few weeks, in hopes that you 
will learn and be enlightened by learning how to build a Solar System, 
from the smallest elements, to the largest Jovian planets.
	Let us begin by looking at Goldschmidts classification of 
elements. V.M. Goldschmidt was a geochemist from the early 1920's who 
became interested in why elemements work the way they do in nature. He 
was, in my view, the founder of the science of geochemistry, and 
cosmochemistry. He describes geochemistry as thus: " The primary purpose 
of geochemistry is on the one hand to determine quantitatively the 
composition of the Earth and it's parts, and on the other to discover the 
laws which control the distribution of the individual elements. To solve 
these problems, the geochemist requires a comprehensive collection of 
anaylitical data on terrestrial materials,such as rocks, waters, and the 
atmosphere; he also uses meteorites, astrophysical data on the 
composition of other cosmic bodies, and geophysical data on the nature of 
the Earth's interior" (Mason 1958). 
	From the above concepts he developed a classification system to 
define the elements, and put them into perspective from a scientific 
point of view. The basic concept is this: elements want to bond in 
certain manners which can be predicted. From this ability to predict the 
arrangements of elements, we can see how elements are arranged, and thus 
provide us with a window into what type of environment the specimen in 
hand formed. It is important to know these patterns, as it will help you 
understand why meteorites are the way they are, and what the environment 
was like in which they formed. 
	Goldschmidt postulated that the three main phases of meteorites 
Stone, Stony iron, and Iron represent the differentiation of the Earth 
(Brownlow 1979). In doing this he began to realize that meteorites can be 
used as primary models to help explain the geochemical behavior of 
elements on all planetary bodies. It must be said, that this 
classification is excellent in allowing to us to predict the what 
elements will be found where, it is not a useful tool to define environments 
of formation in the absolute, rather it guides us in our thinking about 
the larger picture of Solar System composition.
	The classification is as follows:
1. Siderophile(Metal Loving) Elements: Those elements that tend to 
concentrate in metallic iron, such as Ni,and Co.

2. Chalcophile(Sulfur loving) Elements: These tend to concentrate in 
sulfide phases such as troilite in iron meteorites. Examples are Zn, and Cd.

3.Lithophile(rock loving) Elements: These elements tend to concentrate in 
silcate materials(igneous rocks, meteorites ect.). Some examples are, Na, 
K, and Ca.

4. Atmophile(gas loving) Elements: These tend to be found in our 
atmosphere such as N and Ar. 

Above based on Henderson(1982 pp 76).
	The above gives us a foundation to build our understanding of the 
Solar System, and allows us to expect certain elements to availible in 
certain portions of meteorites, and the Earth. We have seen a pattern 
formed, we must now decipher it. Here we will stop, as I will prepare the 
next piece of the puzzle to present to you. Below I have constructed a 
rough chart that shows siderophile, chalcophile, lithophile, and 
atmophile elements. If there are questions please let me know.

Siderophile        Chalcophile         Lithophile           Atmophile
C,P,Fe,Co          Cr, S, Mn,          Si, Mg, Na           H, C, N, 
Ni,Ge,Ir           Ag, Zn, Se          K, Ca, Cl            O, I, Br

 

References:
	Brownlow, Aurthur H. Geochemistry. Prentice Hall Inc Englewood 
                            Cliffs NJ, 498 pp, 1979
       
	Henderson, Paul. Inorganic Geochemistry. Pergammon Press 353 pp,1982
        
	Mason, Brian.  Principles of Geochemistry. John Wiley & Sons, 
                       INC, New York. 310pp, 1958

Frank Stroik
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