Re: I had a hallucination??


"tadchem" <thomas.davidson@xxxxxxx> wrote in message
news:1136588302.489961.181100@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Der alte Hexenmeister wrote:
> "tadchem" <thomas.davidson@xxxxxxx> wrote in message
> news:1136499161.598976.190360@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

<snip>

> > roll downstream. The wear was likely from "rollin' on the river."
>
> Unlikely, since it would be rapidly washed out to sea.

Uncle Jim finds his in arroyos in the southern Arizona desert -
*before* they get washed out to sea.

Unlikely, geological time plays no part in human lifespans.
The southern Arizona desert was once under water.
The Earth is 4 billion years old, not 6000 years as so many
Americans beleive.


> Most rounded pebbles are the result of waves-on-the-beach
> erosion, of which there are countless numbers.

In the Colorado mountains the 'river pebbles' are pretty well rounded
before they have treveled more than a few miles. The best placer
deposits of gold in the Sierra mountains of California are in
well-rounded river gravel.

Geodes are not gravel. We are discussing geodes.
http://antwrp.gsfc.nasa.gov/apod/ap040206.html



> I suspect you are a landlubber, unused to the violence of the
> sea around Britain's coast :-)

I can tell you've never seen the violence of a flash flood in the
desert. :-)

A flash flood will not duplicate incessant waves pounding on a beach.

<snip>

Why snip?
Losing the debate? Some scientist, you are.

<restore>

Keep in mind that the Earth's crust is considerably folded,
the White Cliffs of Dover are cretaceous marine sedimentary
deposits, as are the Virginian Ridge Formation.
http://www.geo.ua.edu/fieldtrips/trip2001/stop7.html


THE BASIC ROCK TYPES
a.. Igneous: The New - rocks which have congealed from a molten mass. They
can either be intrusive, like granite, or extrusive, like basalt (lava).
b.. Sedimentary: The Used - rocks that have formed by consolidation of
organic or inorganic solid fragments, carried by, suspended in, or droppped
by wind, water, or ice and deposited in layers.
c.. Metamorphic: The Refurbished - a rock formed from preexisting solid
rock by mineralogical, structural, and chemical changes in response to
extreme changes in temperature, pressure, and/or shearing stress.



> What is not so easy to understand is the original crystal formation
> of the geode from the original molten state.
> http://www.desertusa.com/magjan98/jan_pap/du_rock_geode.html

The link has it almost right when it says:
"Geodes begin as bubbles in volcanic rock or as animal burrows, tree
roots or mud balls in sedimentary rock. Over time, the outer shell of
the spherical shape hardens, and water containing silica precipitation
forms on the inside walls of the hollow cavity within the geode. The
silica precipitation can contain any variety of dissolved minerals, the
most common being quartz, but amethyst and calcite are also found."

But then it goes completely off-base with the next paragraph:
"Over a period of thousands of years, layers of silica cool, forming
crystals of different minerals within the cavity. Different types of
silica cool at varying temperatures, thus creating layers of different
types of mineral crystals."

The *precipitation* of silica comes from an aqueous solution, which
limits the temperatureto below the critical temperature of water -
about 374° C. Agate is silica with some water mixed in.

Purple amethyst turns to yellow citrine at about 400-500° C -
*irrerversibly* - so that finding agate or amethyst inside a geode is
proof that it has never been severly heated - certainly NOT to the
1700+° C needed to melt silica.

Never rely on only one source of information, unless you are a reckless
journalist.
"Cave ab homine unius libri." [Beware of the man of one book.] - Thomas
Aquinas

Tom Davidson
Richmond, VA

"Cave ab homine unius UNCLE." - Hexenmeister.


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