Ivor and Olive Lewis on mon 18 aug 08
Dear Marian,
This is a fragmnent from a report into the chemistry of Cuprorivaite
and other similar copper bearing minerals.
the Url was
http://cache.search.yahoo.net/search/cache?ei=3DUTF-p=3DCuprorivaite&fr=3D=
sl
v8-&u=3Dwww.slac.stanford.edu/pubs/slacpubs/12000/slac-pub-12232.pdf&w=3D=
c
uprorivaite&d=3DLFwEvxg5RJpw&icp=3D1&.intl=3Dus
Another reliable source gave the general composition of Cuprorivaite
(God bless Sen. Riva, an Italian geologist who collected material from
Visuvius) as being a Hydrated Copper Calcium Silicate.
I just search for a simple Copper Silicate ! ! !
Best regards,
Ivor Lewis.
Redhill,
South Australia.
<<Benzerara3, and Gordon E. Brown, Jr
....two samples from the Congo (#1) and Arizona (#2) (Fig. 3) are also
very similar to these obtained for spertiniite (Cu(OH)2). The
distribution of Cu in these samples is relatively homogeneous at this
multi-micron scale. In addition, EXAFS spectra for all chrysocolla
samples studied are remarkably similar
(Fig. 4). In the Fourier transforms (FT; Fig. 5), the main peak arises
from oxygen first neighbors, centered near 2.3 =C3=85 (backscattering
phase-shift corrected using =E2=80=9CXAFS=E2=80=9D). The medium-range env=
ironment
around Cu in the seven chryocolla samples is characterized by two main
pair correlations, centered near 4 and 5.5 =C3=85 (not corrected for
backscattering phase-shifts). Then, wavelet transforms (WT) of the
k3-weighted normalized EXAFS spectrum for one chrysocolla sample (#2)
is compared to those computed for
dioptase and spertiniite (Fig. 6). There are similarities in the WT=E2=80=
=99s
among these two models and chrysocolla, including a region near k ~
7-9 =C3=85-1(R+=E2=88=86R ~ 5.5 =C3=85), which is clearly related to Cu n=
ext-nearest
neighbors. Finally, STXM images (collected over the energy range
930-950 eV at the Cu L3/2edges; Fig. 7) show highly contrasted domains
50-100 nm in size, which are enriched in divalent copper (Fig. 7c).
Around these copper-rich domains, the less contrasted domains are
depleted in copper. They have to be enriched in silicon
in order to account for the sample stoichiometries. FIGURE 7. STXM
images (at 930 eV) for two chrysocollas (left: #1, Congo; middle; #2,
USA). Scale bar is 1 =C2=B5m (left) and 5 =C2=B5m (middle). Right : Cu L3=
-edge
XANES for the area highlighted on the left figure, which intense white
line is typical of Cu(II). DISCUSSION The XAFS, =C2=B5-XAFS and STXM
information at the K and L3edges of copper in seven samples of
chrysocolla suggests that this mineral is composed of mesoscopic
Cu-rich domains that are similar in structure to Cu(OH)2(spertiniite).
This information is consistent with infra-red spectroscopic
information on chrysocolla [5], which evidenced the presence of
Si-rich amorphous domains (=E2=80=9Cchalcedony=E2=80=9D). Hence, chrysoco=
lla appears
to be a mixture of submicron- to micron-sized spertiniite-like
(Cu-rich) and chalcedony=E2=80=9D-like (Si-rich) domains, as well as mole=
cular
water. Except minor amounts of Al,
Cu2H2Si2O5(OH)4=E2=80=A2nH2O can then be rewritten as 2Cu(OH)2 + 2SiO2 +
(1+n)H2O. The x-ray diffraction of chrysocolla must be close to that
for spertiniite,
which is also orthorhombic. Therefore, chrysocolla might not a
compositionally homogeneous mineral as is generally assumed. Then, its
validity as a unique
mineral species must be reconsidered. >>>
Neon-Cat on mon 18 aug 08
Ivor, this is about Chrysocolla!! (your post)=20
Chrysocolla, Phyllosilicate class (in the "modulated layers with joined =
strips" group), is orthorhombic. Recall, other minerals have different =
crystal systems. So, while many copper minerals are copper silicates, it =
doesn't mean they're kissing cousins - their birth and ancestry is =
different. They'll display different structures, properties, and, most =
importantly, will be formed differently, a fact reflected in their =
bonding properties and associating abilities. In other words, not all =
copper silicates are alike any more than all minerals containing iron =
are alike.=20
And yes, Cuprorivaite can be hydrated (so many things can be hydrated!). =
When I mentioned it in reference to Egyptian Paste, I wrote that =
Cuprorivaite was similar to Egyptian Paste, not identical. Besides, I =
know your fondness for minerals, that's why I threw it in. But that we =
should now trip off into lumping all copper silicates together was never =
my intention - don't go there.
And Ivor, sometimes a gal just doesn't want to "do" science. We gals =
sometimes wish to run off and play with clay, or clean house, or pay =
bills or just plain zone. If you put my name on a post I feel somewhat =
obligated to respond, especially if I feel we are veering off course in =
a major way. Copper silicates cannot all be lumped into one handy =
explanation. And, who knows what we are creating in our glazes? We'd =
need to have someone run some serious testing for that answer and it =
just might be different kiln to kiln.=20
I do like it that you're getting comfortable with the idea of silicates.
I sure didn't care for your "truism" posted under the thread on =
education (bet you thought I didn't notice). Yep, I'm raising the =
smartest Devon Rex in the world - really! Now if I could only teach them =
to sculpt or paint I'd be a wealth woman! Surely you've let go of that =
overworked truism. Haven't you?
Carry on, I'm about to ascend into the attic to hunt for my rolling pin =
so I can roll out some nice colored and striped clay and make something, =
maybe cats with vertical stripes - oughta be way cool! (subtle =
earth-toned stripes - nothing but the best in realism going on here)
Cheers!
Marian
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of Ivor and =
Olive Lewis
Sent: Monday, August 18, 2008 12:54 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Copper Silicate
Dear Marian,
This is a fragmnent from a report into the chemistry of Cuprorivaite
and other similar copper bearing minerals.
the Url was
http://cache.search.yahoo.net/search/cache?ei=3DUTF-p=3DCuprorivaite&fr=3D=
sl
v8-&u=3Dwww.slac.stanford.edu/pubs/slacpubs/12000/slac-pub-12232.pdf&w=3D=
c
uprorivaite&d=3DLFwEvxg5RJpw&icp=3D1&.intl=3Dus
Another reliable source gave the general composition of Cuprorivaite
(God bless Sen. Riva, an Italian geologist who collected material from
Visuvius) as being a Hydrated Copper Calcium Silicate.
I just search for a simple Copper Silicate ! ! !
Best regards,
Ivor Lewis.
Redhill,
South Australia.
<<Benzerara3, and Gordon E. Brown, Jr
....two samples from the Congo (#1) and Arizona (#2) (Fig. 3) are also
very similar to these obtained for spertiniite (Cu(OH)2). The
distribution of Cu in these samples is relatively homogeneous at this
multi-micron scale. In addition, EXAFS spectra for all chrysocolla
samples studied are remarkably similar
(Fig. 4). In the Fourier transforms (FT; Fig. 5), the main peak arises
from oxygen first neighbors, centered near 2.3 =C3=85 (backscattering
phase-shift corrected using "XAFS"). The medium-range environment
around Cu in the seven chryocolla samples is characterized by two main
pair correlations, centered near 4 and 5.5 =C3=85 (not corrected for
backscattering phase-shifts). Then, wavelet transforms (WT) of the
k3-weighted normalized EXAFS spectrum for one chrysocolla sample (#2)
is compared to those computed for
dioptase and spertiniite (Fig. 6). There are similarities in the WT's
among these two models and chrysocolla, including a region near k ~
7-9 =C3=85-1(R+=E2=88=86R ~ 5.5 =C3=85), which is clearly related to Cu =
next-nearest
neighbors. Finally, STXM images (collected over the energy range
930-950 eV at the Cu L3/2edges; Fig. 7) show highly contrasted domains
50-100 nm in size, which are enriched in divalent copper (Fig. 7c).
Around these copper-rich domains, the less contrasted domains are
depleted in copper. They have to be enriched in silicon
in order to account for the sample stoichiometries. FIGURE 7. STXM
images (at 930 eV) for two chrysocollas (left: #1, Congo; middle; #2,
USA). Scale bar is 1 =C2=B5m (left) and 5 =C2=B5m (middle). Right : Cu =
L3-edge
XANES for the area highlighted on the left figure, which intense white
line is typical of Cu(II). DISCUSSION The XAFS, =C2=B5-XAFS and STXM
information at the K and L3edges of copper in seven samples of
chrysocolla suggests that this mineral is composed of mesoscopic
Cu-rich domains that are similar in structure to Cu(OH)2(spertiniite).
This information is consistent with infra-red spectroscopic
information on chrysocolla [5], which evidenced the presence of
Si-rich amorphous domains ("chalcedony"). Hence, chrysocolla appears
to be a mixture of submicron- to micron-sized spertiniite-like
(Cu-rich) and chalcedony"-like (Si-rich) domains, as well as molecular
water. Except minor amounts of Al,
Cu2H2Si2O5(OH)4=E2=80=A2nH2O can then be rewritten as 2Cu(OH)2 + 2SiO2 +
(1+n)H2O. The x-ray diffraction of chrysocolla must be close to that
for spertiniite,
which is also orthorhombic. Therefore, chrysocolla might not a
compositionally homogeneous mineral as is generally assumed. Then, its
validity as a unique
mineral species must be reconsidered. >>>
| |
|
