Why No Granite? Options

[dvandorn]

Grooooaaaaaannnnnnnnnn....



-the other Doug

[Bill Harris]

Edstrick-- great explanations. The Earth is a wonderful crockpot, no?

Elk Grove-- behave. That was not a gneiss thing to say.



--Bill

[ElkGroveDan]

Elk Grove-- behave.  That was not a gneiss thing to say.

I really don't give a schist what you think.

[dvandorn]

Yeah -- on this subject, that's enough gab, bro...

-the other Doug

[Bill Harris]

OK, allrite, don't get uptite, I'll get outasite.

--Bill

[lyford]

*Ouch*

[edstrick]

"Coal is Medieval, it's black and primeval,
Diamonds are colder than ice.
Granite's a bedrock, a stone for the dead rock,
It's... not... gneiss!"

There's an entire filksong on this... I've got a tape with it sung by Juanita Coulson, entirely filled with geologic puns. This is the only verse from "It's Not Gneiss" I immediately find online.

[The Messenger]

Throughout all of it there are small chunks of "metal", and there is definately repulsion.  so its not the screws underneath, but thanks anyway.

Well, that's an Ah Ha moment. The metal chunks are inclusions that probably are magnitite - a good rock dude could probably tell you where the granite was quarried.

During WWII, the Japanese launched into the jet stream a mechanical hot air balloon attack on the US west coast. (It was ingenious, but Bruce would call it cheap.) The bombs had an altimeter tied to a ballast and a throttle, and many of them made it to the west coast and caused one death, when a kid on a picnic picked up an unexploded bomb.

In the US, the ballast sand was taken to geologists, who compared them with sand samples from Japanese beaches. They were able isolate the source to a single river alluvial deposits, identified a likely production facility, and bombed it.

[maryalien]

well after more digging around (of course i should be working) i found out that "technically" what i have is Larvikite, not a true granite but indiginously igneous anyway and is quarried in Norway and there are veins of magnitite there also, so i guess you were all right anyway! go figure...(ha ha)

so thats enough from me. i hope theres not "anorthoclase" of granite/metal findings. HA HA, I TRIED, believe me it took me a long time...

mar

[CosmicRocker]

I really did enjoy those summaries, edstrick. Truly, I did. They made up a nice "refresher course" that reminded me of some things from igneous petrology that I had long forgotten (or more accurately, had misplaced, somewhere in my memory banks). But in my defense, that was a long time ago. In fact, my professor from that class claimed that he actually witnessed the first occurance of a Precambrian schist hitting an alluvial fan.

That magnetic granite counter top intrigued me, but now I see it's not a granite at all, but probably something more akin to anorthosite...one of the mafic feedstocks to the fractional crystallization processes that eventually create true granites. The counter-top and construction stone industries have commercialized the term "granite" beyond all normal recognition. It's a nice looking rock though, with the irridescent reflections. It reminds me of Labradorite, but other feldspars can display the effect.

At least the weak magnetic properties of that stone now make sense. Such mafic rocks are likely to contain a fair amount of magnetite.

[edstrick]

Earth has generated a bogglaceous variety of "weird rocks". That magnetic "granite" is one of them, it seems.

Some of them are the result of reasonably normal magmas eating (assimilating) another rock and ending up with very weird chemistry. You can get carbonatite volcanic rocks, at least some of which form when magma eats a lot of limestone and you actually have black lava flows with carbonate minerals in them that turn white (on the surface) as they cool. There's one active carbonatite volcano in Africa, I don't recall if it's carbonates come from assimilated limestone or what.

Others are the result of poorly understood processes in the mantle, maybe or maybe not involving subducted crust. One thing I learned about in Igneous Petrology back around 1979 were the existance of "Feldspathoid" igneous rocks. They make up a teeny tiny fraction of all igneous rocks, but a good fraction of the different petrologic types. Sometimes, for reasons that were not understood worth diddly back then (I have no idea about now), igneous melts are produced that are aluminum-deficient. Instead of producing normal feldspar minerals in the calcium/sodium/potassium feldspar mixing series, you get "weird" silicates that have fewer aluminum atoms than normal igneous minerals, things like nephelinite, sodalite, i-cant-remember-ite. Some of the minerals normally only show up in metamorphic rocks where the sediments that got cooked were considerably changed from original weathered igneous rock in composition. Here they're showing up in rocks formed from melt. What makes such weird melt.. I don't know. I don't know if anybody knows yet.

The weirdness of the feldspathoid igneous rocks came to mind when there was a recent discussion on exoplanets that might be more carbon-rich than our solar system's planets, ending up perhaps with silicon-carbide mantles and asphalt covered crusts. Gonna be a lot of surprises.

[Bill Harris]

Indeed, thanks for the refresher. My ig-met-pet coursework goes back farther than yours and for the last quarter of a century I've been slogging thru Carboniferous deltas...

When you start to heat, reheat and recycle rocks with a dash of hydrothermal fluids you can get wild results. We can only imagine, and barely so, what is on alien worlds...

--Bill

[edstrick]

I'm staking a claim on Io. Ghods.. the mineral collector's paradise that must be there.............

[Bill Harris]

I can imagine! Io would be better than Arkansas.

Sulfide minerals generally make beautiful crystals.

--Bill

[Guest_BruceMoomaw_*]

What's this "ghods" business all the time, Ed? Are you worshipping aliens and not telling us about it? DHS has a place for people like you...