"hanson" skrev i en meddelelse
news:_kIQf.196$Km6.54@trnddc01...
element or compound in tree bark that it burns with too much ash

"Bob" wrote in message
...
"Farooq W"
| More surprising the uptake of heavy metals especially
| Th and U by the plants...Barium is abnormally high or the
| soil on which that tree grew was rich in barium ores!

On Sat, 11 Mar 2006 02:27:31 GMT, "donald haarmann"
wrote:
The up take of uranium by plants is well know. See for example :-
Botanical Prospecting for Uranium on La Ventana Mesa, Sandoval
County New Mexico. US Geological Survey Bulletin 1009-M. 1956.
Some plants uptake serious amounts of selenium.

[Bob]
A Berkeley group is developing the use of a plant for Se
decontamination of soil. It is in field testing. (I could probably
find a ref if someone wants it.)
Then there are the Ni accumulators, which have several percent Ni in
their sap, nicely chelated (citrate, I think).
bob

[hanson]
=1= I posted this into sci.geo.geology in hope to get some views
from the geos' camp about the popularity & effectiveness of BP.
=2= As what/which compound does Si get into solution from the
calcogen silicates, considering that SiO4-- is stable only at
pH 11 in aq?
=3= in what soluble or sol-gel form is Silicon taken up
and transported in/to the plant (at a pH range ~ 7)
=4= As what/which compound is Si stored in the plant?
=5= and what function does the Si have in the plants?

I cann't answer your questions, but I've googled something from the
geological perspective.

I havn't read this ... it looks promising
http://www2.warwick.ac.uk/fac/sci/bi...ezsilica03.pdf

My own comment. quote
Si++++ makes a geometrically favorably
binding with O in the sense that it perfectly fits the dimple between 4O
atoms stacked as a pyramid. Al+++ is a small ion too and has exchange with
Si. In silicates the SiO4---- tetraedron are considered a building-block,
and it has any imaginary crystaline combination with metals, from pairs of
tetraeder sharing one O and saturates other bindings with Fe++ or Mg++
through to chains, rings, sheets and frameworks sharing more corners
depending of availabillity of Si.
Unquote

Halfway down the page is an electron microscopic image of opal
http://www.grahamblackopal.com/webcontent10.htm

My comment:
I don't think that anyone knows why these tiny puff-balls of silica forms in
such an ordered way. It is basically this mystery and that it could be
biologically mediated that cause me to ponder and respond.

This beetle knows how
http://www.gbjewelers.com/education/...al-beetle.html

Replacement by opal. Fossilized wood. Opalisation is a core process that
generates a host of semi-precious stones.
http://www.microscopy-online.com/Ven.../Stereo/5b.jpg

Opal (disordered hydrated silica)
http://www.galleries.com/minerals/mi.../opal/opal.htm
quote
Although there is no crystal structure, (meaning a regular arrangement of
atoms) opal does possess a structure nonetheless. Random chains of silicon
and oxygen are packed into extraordinarily tiny spheres. These spheres in
most Opals are irregular in size and inconsistent in concentration. Yet in
Precious Opal, the variety used most often in jewelry, there are many
organized pockets of the spheres. These pockets contain spheres of
approximately equal size and have a regular concentration, or structure, of
the spheres.
unquote

General info on flint and chert
http://www.abdn.ac.uk/geospatial/sum...factsheet1.htm

Quote
Cryptocrystalline Quartz

Cryptocrystalline quartz is simply quartz whose crystals are so small that
they can only be seen with the aid of a high-power microscope. It is formed
geologically from silica that has dissolved from silicate materials. Over
geological time, this amorphous silica gel dehydrates to form microscopic
crystals and eventually becomes what we know physically as rock.
Cryptocrystalline quartz occurs in many varieties. These varieties have been
named based on their color, opacity, banding and other observable physical
features. Technically speaking, the two varieties that account for the vast
majority of "flint" artifact materials are chalcedony and chert.

Other varieties encountered in the artifact world are agate, jasper and
petrified wood. Interestingly, petrified wood is usually wood that has becn
replaced by agate. This same process also occurs with coral, hence the term
"agatized coral".

Chalcedony Chert and Flint

Chalcedony is a variety of cryptocrystalline quartz with extremely small
crystals and a specific gravity (weight under water, a measure of a
rock/mineral's purity) nearly identical to that of pure quartz. Due to its
very high quartz content and super fine particle matrix, chalcedony has a
very waxy luster.

Chert is composed of larger crystal particles and has a specific gravity
similar that of pure quartz. Due to impurities and larger particle sizes,
chert is somewhat less "quartz-like" than chalcedony. Chert is duller and
more opaque than chalcedony and its luster ranges from non-existant to very
waxy, depending on the individual rock formation.

So what is flint? By mineralogical definition, flint is simply black chert.
It appears that the term "flint" was originally applied to the high quality
black cherts found in England. Over the years names have evolved for local
chert formations/deposits that may include the word "flint" and technically
speaking these would be incorrect more oflen than not. The reality of the
flint verses chert debate is that in most cases it is something like
"splitting hairs", there really is very little difference, chemically
speaking. Artifact collectors tend to call materials that have a more waxy
luster "flints" and those which have less luster to no luster "cherts". The
difference between them lyes in their purity relative to pure quartz and
their matrix particle size. The smaller the particle size and the purer the
material, the more likely we collectors would be to call the material flint.
To a purist, we would be wrong. A generalist would say "close enough".
Note: Some examples of Flint Ridge Flint are known to be 98.93 % pure
silicon dioxide.
Unquote


Carsten