[Rockhounds] Question

[DonH]

pmodreski at aol.com wrote:



> The Broken Hill Pb-bearing orthoclase is well known for its fluorescence


I'm not sure how well-known it is; I could originally find little on it. 
   I suppose my definition of "well known" is whether you can find a 
number of specimens for sale via fl. mineral dealers, and whether the 
collectors I know have either heard of it or have one in their 
collection.  Admittedly that is a very biased definition.
I am preparing a small article for an Australian publication on this; it 
might be known but deserves to be refreshed.  I got one mediocre and one 
really nice photo of two different fluorescences from two different 
localities in the district.

 > What do they know about the oxidation state of the lead in the 
orthoclase, and is it most correct to refer to it as "plumbian" or 
"plumboan"?

Here is info from one of the abstracts, I believe provided by one of our 
list members a few months ago.  Note that I heartily disapprove of 
calling it amazonite, since that is a separate variety with a distinct 
legacy of meaning, and to call this BH NSW material amazonite will only 
cause confusion and anguish.  As far as plumbian or plumboan, I must 
scramble to dig out the IMA guidelines on adjectival modifiers to see if 
these are used for distinction or whether "plumbian" covers all general 
cases of lead-rich minerals.  I can never remember the slight 
distinctions in the wording and I'm glad that terms like ferric and 
ferrous, cupric and cuprous, have been superceded by terms like "Fe 
(II)" and "Fe (III)" and "diavelent" and "trivalent", etc.


"Solubility and behavior of lead in green orthoclase (amazonite) from 
Broken Hill, New South Wales, Australia.  Murakami, Hideki; Takashima, 
Isao; Nishida, Norimasa; Shimoda, Susumu; Matsubara, Satoshi.  Research 
Institute of Materials and Resources, Faculty of Engineering and 
Resource Science, Akita University, Akita,  Japan.  Ganko  (2000), 
95(3),  71-84.

The soly. and behavior of lead in feldspar are elucidated by EPMA and 
XPS (also known as ESCA) analyses for green orthoclase (amazonite) from 
Broken Hill, New South Wales, Australia.  The role in the crystal 
structure establishes Pb cation as PbAl2Si2O8 end member for the 
orthoclase solid soln., and the max. quantity of PbAl2Si2O8 is 3.8 mol% 
in the green orthoclase.  The lead cations, except the one existing in 
the orthoclase lattice, namely structurally bound Pb, occur in the green 
orthoclase by the following two ways;

     	1) as galena inclusions, and
  	2) as unidentified Pb-bearing micro-inclusions.

The chem. shift for Pb atom in the green orthoclase was  investigated by 
XPS, and compared with those in a Pb-metal, Pb-oxides, and a galena. 
Differences in the binding energy between Pb in the green orthoclase and 
other Pb-substances show distinctly that most of the Pb is not present 
as impurities like micro-minerals, but as structural components in green 
orthoclase.  Crystal chem. consideration of Pb affords us infallible 
discrimination of soly. of PbAl2Si2O8 end member rather than PbAlSi3O8. 
  The existence of PbAl2Si2O8 as the main end member in green orthoclase 
exhibits the charge-coupled substitution in the extra framework and the
tetrahedral site; K++Si4+ .tautm. Pb2++Al3+.  Inhomogeneous distribution 
of Pb cation within the single crystal shows that the condition of Pb 
cation in green orthoclase structure is unstable."