Why do igneous rock types become more complicated with time?

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Offline JimBob

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What are they thinking???? Don't these guys have anything better to do??

"The International Union of Geological Sciences (IUGS): Subcommission on the Systematics of Igneous Rocks" has a classification of igneous rock, both intrusive and extrusive, that is simply Byzantine! It is much more complicated that it was when I was in school - albeit in the dark ages 40 years ago (mineralogy course in 1968.) I needed to know only about 30 rock types. Now there are 50 or so.

I had it hard enough keeping a syenite unconfused with a trachyte. They didn't have quartz or feldspathoids in their names. Now I need to know if it is a regular syenite or trachyte and if it is a quartz- or foid- syenite or trachyte.  ("foid" is what were called feldspathoids; feldspathoids was too difficult to say, I guess. Complicate most things, but if you have a speech impediment - just simplify the term.)

Why is all of this necessary?

The preferred Folk Carbonate Classification was published in 1959 and has  not been revised since I was in school. The Dunham classification was published in 1971 but is less precise (But this can be a blessing if you are in the field.)

So why did igneous rocks need to be reclassified? And why so complicated????????


« Last Edit: 06/08/2009 02:42:05 by JimBob »
The mind is like a parachute. It works best when open.  -- A. Einstein

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Offline LeeE

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Perhaps they've caught Politician's Disease.  This ailment deludes the sufferer into needing to pointlessly change things under the pretext that they're improving the world, but in reality it is just to prove to themselves that they exist.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline wanhafizi

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Why do igneous rock types become more complicated with time?
« Reply #2 on: 06/08/2009 11:54:31 »
Perhaps they've caught Politician's Disease.  This ailment deludes the sufferer into needing to pointlessly change things under the pretext that they're improving the world, but in reality it is just to prove to themselves that they exist.

I love it. It's so true...

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Offline Bass

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Why do igneous rock types become more complicated with time?
« Reply #3 on: 06/08/2009 19:43:26 »
Perhaps they've caught Politician's Disease.  This ailment deludes the sufferer into needing to pointlessly change things under the pretext that they're improving the world, but in reality it is just to prove to themselves that they exist.

HEY!  I resemble that remark!

I believe the "foids" were foisted upon us because the presence of different types of feldspathoids have genetic connotations for these unique magmas.

But I agree with JimBob- who has time to remember all those names?  It's almost as bad as all the genus, family, order, etc for dead animals that the paleontologists have to memorize.
Old enough to have a grandson
Slow enough to study rocks
Thirsty enough to find a pub

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Offline JimBob

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Why do igneous rock types become more complicated with time?
« Reply #4 on: 06/08/2009 22:10:56 »
At least there is a "logical" explication - BUT I also think that politician's disease has taken over the logic.

What happened to the few descriptive terms -  granite, rhyolite, basalt, etc.?

IN FACT THERE IS NO MORE BASALT - according to this inane committee. It is now "basaltoid." (http://en.wikipedia.org/wiki/QAPF_diagram)

Gosh, I am going to miss Pahoehoe.

The mind is like a parachute. It works best when open.  -- A. Einstein

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Offline Geoman69

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Why do igneous rock types become more complicated with time?
« Reply #5 on: 07/08/2009 06:01:43 »
At least there is a "logical" explication - BUT I also think that politician's disease has taken over the logic.

What happened to the few descriptive terms -  granite, rhyolite, basalt, etc.?

IN FACT THERE IS NO MORE BASALT - according to this inane committee. It is now "basaltoid." (http://en.wikipedia.org/wiki/QAPF_diagram)

Gosh, I am going to miss Pahoehoe.



They're still there, just not in the "field classification" (see figures 1 and 2 on the link you posted).  Apparently in the field, you're just supposed to throw an "oid" behind whatever you find.  In other news, Foiditoid might be my new favorite term  [;D] .
« Last Edit: 07/08/2009 06:03:43 by Geoman69 »