Talk:Kimberlite
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[edit] Comment
Kimberlite is found in extinct volcanoes. Within the kimberlite are found naturally occuring diamonds. The name comes from Kimberly, South Africa where it was first discovered that diamonds are found in this geological material.
I changed "Σcarbon dioxide" in
- The mineralogy of Group II kimberlites may represent a similar melting environment to that of Group I kimberlites, the difference in mineralogy being caused by the preponderance of water versus Σcarbon dioxide.
to "carbon dioxide". I don't know what "Σcarbon dioxide" is or whether it even exists. AxelBoldt 22:41, 18 April 2006 (UTC)
Sigma is used to represent "total" so it meant "total CO2". In case you wanted to know. Rolinator 01:18, 19 April 2006 (UTC)
Yes, thanks, that's interesting. Should we put it back in then? I wonder whether the Sigma adds anything to the meaning of the sentence though. I suppose we wouldn't talk about "Σwater" either. AxelBoldt 22:16, 19 April 2006 (UTC)
Well, it's a measure of CO2, which is how carbon is reported in the laboratory. When doing a CIPW Norm, you only get a list of ingredients, and you don't neccessarily know if they go into any particular mineral until you work through the norm. CIPW norms don't always work well on these rare rocks because the mineral phase diagrams which the norm is predicated upon, are poorly constrained at depths (ie; Pressure and Temperature) which generate kimberlites, for a start. Secondly, the mineralogy in the rocks is diagnostic of high pressures. In a rock of the same composition generated at shallower depths you may get different minerals. The prime example of this is silica undersaturated high-alumina basalts which are normative for olivine but sometimes contain pyroxene and nepheline (not the predicted olivine); the the CIPW norm will derive an estimated mineralogy but it may differ from the observed. The amount of CO2 in the system for a kimberlite is diagnostic; it may be present in the carbonate minerals, as graphite (which is analysed as CO2 because it is oxidised during analysis, hence giving a false CIPW estimate of carbonate abundance if one assumes all CO2 is present in carbonates), and even as CO2 trapped in pores and inclusions and hydrous phases (especially phlogopite mica). Thus why the sum of CO2 is used, because it is diagnostic of this kind of rock as opposed to Lamproite and some lamprophyres or alkali basalts. It could therefore be put back in; maybe with a footnote explaining this. Or at least with a link to this talk age and the above explanation. Rolinator 01:15, 20 April 2006 (UTC)
- Great, I learned a bit there. I've done CIPW calculations (by hand :-) just not for these exotic rock types. However, I'd guess that most readers would be lost here. So we would need a more simplified and/or detailed explanation - plus an article on normative mineralogic calculations as well as those four CIPW guys. So maybe rather than a footnote - a link to an explanatory article would be better. Vsmith 01:38, 20 April 2006 (UTC)
- Yeah. CIPW norms are a major headache. There are a few free to air CIPW norm calculators. Most work with silica saturated rocks with a primarily hydrous vapor phase. In the end, the CIPW norm is best used to describe aphanitic rocks...as was first intended...but its often useful for rocks with a lot of groundmass minerals. Like Kimberlites. I also cleaned up the above...7 a.m. chicken scratchings and all that jazz. I'll have a look over what's on the CIPW norms page.Rolinator 05:24, 20 April 2006 (UTC)
[edit] Precursors
I removed;
Kimberlites are a signature mineral for diamonds, and as such are of great 'cursor' value to diamond miners/prospectors. There is a large amount of ongoing research taking place regarding Kimberlites as a diamond 'precursor', Lisa Windsor of Bristol University being one of the academic researchers foremost in this field.
for several reasons. Firstly, we need a link, or it's just hearsay. Secondly, kimberlite is not a mineral it is a rock. And it is not a precursor for diamond, it is the hosst of diamonds, although it would be more correct to say it is the material which brings diamonds to the surface, and that the mantle itself is the source of diamonds. And to say that finding a kimberlite leads a diamond prospector to diamonds is at best redundant, regardless of whtever you meant by'cursor value.
In terms of what I suggest; get a link, and we can talk about indicator minerals versus kimberlites as an exploration tool.Rolinator 06:10, 16 December 2006 (UTC)
Check out normative mineralogy. Rolinator 06:57, 20 April 2006 (UTC)
[edit] Copyright violation from Oct. 2007 removed
I've removed a copyright violation from http://www.geology.ubc.ca/research/diamonds/kopylova/intro/definition.html and related pages which was added by User:Rananjay on 18 October 2007 (the user's only article edits were on that date). Some of the material was a direct copy/paste from that website whereas other added material was from elsewhere. The above website is a valid source and is included in the reference section and would serve as a source for properly expanding the article, but not as a direct copy. Vsmith (talk) 01:45, 21 January 2008 (UTC)
