That rock is a bit small to make a good ID. It definitely looks like a matrix-supported conglomerate, with and outside possibility a lapilli tuff to agglomerate. Without the larger context of where it's from (and I'm not assuming dojmo is incorrect) it's tough to make the actual call based on a photo.

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I agree that you'd have to do some mineralogical analysis to narrow down what species of feldspar it is. But, I tend to think it is orthoclase. Quite an interesting igneous intrusion, nonetheless.

Eric

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Details, details.

The friend that picked the rock up just looked down and decided it would be a good rock to take back to me, and I appreciate it. However, the flickr link does allow a fair amount of enlargement.

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"Quaerendo inventis"

Here's an outcrop I found just this last summer just outside Oolitic, IN. As it turned out it just happened to be a prehistoric coral reef dating back to the Silurian through Devonian. From this outcrop I was able to extract the fossil pictured below which contains polypora (coral) and scallop-like shells.

Attached Images

	outcrop.jpg (76.2 KB, 5 views)
	polypora_01.jpg (53.5 KB, 5 views)

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I see Brachiopods.

Nice piece.

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"Quaerendo inventis"

If you're having trouble viewing the full-sized image of the fossil from the thumbnail as am I, here's another image of it.

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Thanks, jlhredshift. But actually what looks like Brachiopods is one of two types of Polypora, which may be more apparent in the larger image.

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I did blow up the flickr photo as much as possible on the site. There really is no substitute for standing right at the outcrop with a hammer and a hand lens.

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I couldn't agree more, teddyv!

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Well, I am referring to what you have described as "scallop".

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"Quaerendo inventis"

Are you referring to the larger, fan-shaped fossil at center-right of the rock?

You mean the trace fossil at the bottom right edge? That is a scallop-like fossil. All the rest are polypora. If you could see the fossil yourself under magnification you would see that I am right. Believe me, I've analyzed and researched this particular specimen at great length.

Eric

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The larger fan-shaped fossil at center-right is one of two types of polypora in this specimen. Believe me, I have researched this specimen at great length. It is a type of polypora. Of that I am certain. You really have to see the specimen in person.

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I certainly do not claim to be an expert on polypora. A higher resolution picture might be interesting.

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"Quaerendo inventis"

And it's been a long time since my paleontology courses, so I can't add too much to this discussion.

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I wish I had one, jlhredshift. But believe me when I say it was hard enough just getting this shot! LOL

Eric

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I believe you.

If I was to speculate, I'd guess the fossil towards the center-left is a brachiopod.

Now, that's a possibility! Unfortunately, there isn't enough of it left to be certain.

Eric

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Well, now I've had to crack open my paleontology textbook. The fossil on the left seems to be exhibiting a delthyrial opening, looking kind of like head-on to a manta ray.

Gray and Granitic Gneiss. This one was just a little bit too big to fit into my backpack! LOL I love metamorphic rocks!


Gray and Granitic Gneiss

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Metamorphic rocks are probably my favourite group as well. There are just more interesting minerals in the assemblages. Although a current project we are working on has some of the nastiest group of rocks as far as identification we've come across. There is something like 3 or 4 deformation phases and 3 alteration events. We think the protolith is mostly volcanic with some sediments, but nobody can really tell for sure.

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The word "tortured" comes to mind.

Pictures, possibly???

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(By the way, I hate it that so many papers in the areas of planetary science and geology are not easily available to the dreaded "non-subscribers". It is like they are screaming at me: "YOU CAN'T HANDLE THE TRUTH". Good, I feel better now.)

"Quaerendo inventis"

Yes, metamorphic petrology, I believe, is the toughest of the three branches of petrology, simply because of the complexities involved. These rocks many times have undergone such extreme deformations and transformations that it can be extremely difficult, to put it mildly, to figure out what was there to begin with. I've seen groups of rocks like that ones to which you referred that stubbornly defy analysis. This is probably why so many field geologists avoid studying metamorphic rocks. I love them even though they can be a royal pain to try to understand.

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I’ll see if I can post something. Since they are technically our client’s property I’ll need to confirm that I could post something like that.

Metamorphic petrology was probably my favourite class through university of my university. For some reason the physical and chemical processes just seemed to make sense. Of course in the real world, things are never as cut and dried. We love to identify by protolith whenever possible. I think we've had 3 Ph.D's, a couple Master's and a raft of professional geologists pass through and make their opinions. Basically it comes down to: the rocks cannot be identified by the protolith. So we have been trying to use our geochemical data to attempt to discriminate the lithologies but with very limited success. We joked that the analysis was more voodoo witchcraft, but then that also summarizes geophysics.

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LOL Indeed it does, teddy! Some still refer to radiometric dating, for example, as the "black art"! hehe

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My geology summer field class mapped an area that had undergone a series of events - folding, faulting and igneous intrusion with accompanying contact metamorphism. It was a bear to work it all out.

Hi guys, I hope nobody minds yet another meta-discussion, but I have a hydrology question I'd like to put to the experts.

A long time ago I studied hard to get good at raising tropical fish, eventually becoming a master fish breeder, (though woefully out of date nowadays).

Now the majority of your spectacular freshwater species come from soft acidic waters such as those found in the Amazon basin and tropical rivers world wide. And the reason the waters of the Amazon were so soft, or so I read, was since the area had been a rain forest for the last 33 to 27 million years, all the carbonates and such had been washed out already.

Well lately, thirty years later, I've been thinking this was a gross over-simplification of the issue and have been trying to deepen my understanding of it. I started to suspect this was the case when I saw a documentary on caving in Borneo/Indonesia, who rainforests are some of the oldest in the world at 110 million years old and they still have plenty of limestone. AND their rivers are soft and acidic as well.

I wonder, and am beginning to suspect, if it's:

A) Just the volume of water from the rain keeping the concentrations low.

B) The huge biomass of plant life sucking the soluble minerals out of the solution.

C) At least in the case of the Amazon, there wasn't a lot of carbonates to begin with.

D) all the above.

I know the low pH is due to both the solubility of the CO2 into the rain AND the peats and tannins from the jungle soils. My cardinal tetras would all start spawning when I dropped the pH to just under 6, using de-ionized water and tannins. (In the wild they will spawn in waters with a pH as low as 4.5. Protects their eggs from bacteria and fungus.)

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I think you were misinformed there, BD -
as at the turn of the millennium (when I was looking at a similar question):

a) The Amazon discharges 7245 x 10¹² L/yr @ 20 mg/L DIC (Dissolved Inorganic Carbon) >> 1.45 x 10¹⁴ g/yr, or ~ 36.34% of the world riverine total discharge of DIC

b) The Yangtse discharges 1063 x 10¹² L/yr @ 148 mg/L DIC (Dissolved Inorganic Carbon) >> 1.57 x 10¹⁴ g/yr, or ~ 40.26% of the world riverine total discharge of DIC

c) These two rivers therefore represent more than 3/4 of the world total DIC riverine discharge ...
(source - assignment paper, Flinders University)


D) ... or even E) all of the above, plus other factors ...

such as the alkali-acid balance of the TDS (Total Dissolved Solids) of the discharge waters -

The two rivers also transport similar masses of calcium and magnesium. The Yangtse shifts 1.5x the mass of sulfate compared to the Amazon, but the Amazon moves 2.5x the mass of sodium, 1.9x the chlorine, 4.67x potassium, and 8.69x silica. Clearly, these two rivers are draining and eroding very different geological landscapes.
(source - assignment paper, Flinders University)

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We just returned from a weekend in New York City and we visited the American Museum of Natural History. In the main entrance are a set of columns that are just magnificent.



This is a closeup and here is the link to Flickr where it can be enlarged substantially.

I am going to call it marble, with reservations, and the geologic history of its formation is obviously complicated. I have purposely not researched it.

The amount of different rocks that are on display being used as building material is unending as one wanders the canyons of New York City. In Central Park there are exposures of Manhattan Schist wherein you can see stratification and in one instance I saw an unconformable contact of feldspathic white and pink granite with the schist, being used as a curb material. At night driving by the exposures of the schist it would glisten with reflections of light off of the crystals contained in the schist.

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"Quaerendo inventis"

I got to say that it looks almost fake (or at least not natural). The distribution of the larger fragments just looks to regular.

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