the Solar System:
A Look at Element Classification
by Frank Stroik
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 (while) 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.
C, P, Fe, Co
Ni, Ge, Ir
Cr, S, Mn
Ag, Zn, Se
Si, Mg, Na
K, Ca, Cl
H, C, N
O, I, Br
Brownlow, Aurthur H. Geochemistry. Prentice Hall Inc
Englewood Cliffs NJ, 498 pp, 1979
Henderson, Paul. Inorganic Geochemistry. Pergammon Press 353
Mason, Brian. Principles of Geochemistry. John Wiley & Sons,
INC, New York. 310pp, 1958