Hi,
I have a variety of minerals from Ward's in the lab that I am contemplating to mount as possible (primary or secondary) mineral standards. Before I go through that exercise and find out that they do not make good standards, I thought I ask here first.
Does anyone has any opinion or experience with any of the following minerals as a good (or bad) microbeam standard (descriptions from the label):
- Hornblende (495917) Gore Mountain, New York
- Augite (495858) Harcourt Twp., Ontario[/li][/list]
- Diopside (495870) Fianarantsoa, Madagaskar
- Enstatite (492125), Bamble, Norway
- Microcline (495918) Richardson Quarry, Ontario
- Labradorite, Harney Co. Oregon
- Corundum (495868), Yogo Gulch, Montana (not sure about that one, I heard bad things about Corundum as standard in general, correct?)
- Dolomite (495871), Butte, Montana
- Calcite (495860), Santa Eulalia, Chihuahua, Mexico
- Sphalerite (495890), Picos de Europa, Spain
- Pyrite (495884), Huanzala, Peru
- Chalcopyrite 495863, Messina, Transvaal
- Chalcocite, Messina, Transvaal
Thank you!
Anette
Hi Anette,
This is exactly what I started trying to do a few years ago, but I only choose their wollastonite material from Willsboro, NY. It is very clean material.
Here are the analyses I did using our Chesterman diopside as a standard for Ca and SiO2 as a standard for Si (only printing out the statistically significant digits for the concentrations):
Un 5 Wollastonsite (Willsboro,NY) majors, traverse
TakeOff = 40.0 KiloVolt = 15.0 Beam Current = 20.0 Beam Size = 20
(Magnification (analytical) = 24000), Beam Mode = Analog Spot
(Magnification (default) = 600, Magnification (imaging) = 100)
Image Shift (X,Y): .00, .00
Number of Data Lines: 13 Number of 'Good' Data Lines: 13
First/Last Date-Time: 10/03/2007 11:16:48 AM to 10/03/2007 11:43:26 AM
WARNING- Using Alternating On and Off Peak Acquisition
Average Total Oxygen: 41.304 Average Total Weight%: 99.866
Average Calculated Oxygen: 41.304 Average Atomic Number: 13.582
Average Excess Oxygen: .000 Average Atomic Weight: 23.221
Average ZAF Iteration: 3.00 Average Quant Iterate: 2.00
Oxygen Calculated by Cation Stoichiometry and Included in the Matrix Correction
Un 5 Wollastonsite (Willsboro,NY) majors, traverse, Results in Elemental Weight Percents
ELEM: Ca Si O
TYPE: ANAL ANAL CALC
BGDS: LIN LIN
TIME: 60.00 60.00
BEAM: 20.01 20.01
ELEM: Ca Si O SUM
180 34.2 24.3 41.304 99.8
181 34.3 24.1 41.188 99.6
182 34.5 24.2 41.324 100.0
183 34.2 24.1 41.110 99.4
184 34.3 24.4 41.469 100.2
185 34.2 24.2 41.203 99.6
186 34.4 24.3 41.368 100.0
187 34.4 24.2 41.311 99.9
188 34.3 24.1 41.195 99.7
189 34.3 24.0 41.026 99.3
190 34.4 24.3 41.456 100.2
191 34.6 24.3 41.461 100.3
192 34.4 24.4 41.541 100.3
AVER: 34.3 24.2 41.304 99.87
SDEV: .115 .121 .155 .334
SERR: .032 .033 .043
%RSD: .334 .498 .374
STDS: 358 14 0
STKF: .1693 .4101 .0000
STCT: 2297.1 23650.7 .0
UNKF: .3199 .2071 .0000
UNCT: 4339.3 11941.6 .0
UNBG: 126.5 44.9 .0
ZCOR: 1.0737 1.1697 .0000
KRAW: 1.889 .505 .000
PKBG: 35.305 267.612 .000
Un 5 Wollastonsite (Willsboro,NY) majors, traverse, Results Based on Sum of 2 Cations
ELEM: Ca Si O SUM
180 .995 1.01 3.005 5.005
181 .999 1.00 3.001 5.001
182 .999 1.00 3.001 5.001
183 .997 1.00 3.003 5.003
184 .993 1.01 3.007 5.007
185 .995 1.01 3.005 5.005
186 .996 1.00 3.004 5.004
187 .998 1.00 3.002 5.002
188 .999 1.00 3.001 5.001
189 1.00 .999 2.999 4.999
190 .994 1.01 3.006 5.006
191 1.00 1.00 3.000 5.000
192 .993 1.01 3.007 5.007
AVER: .997 1.00 3.003 5.0032
SDEV: .003 .003 .003 .003
SERR: .001 .001 .001
%RSD: .267 .265 .089
Range of Homogeneity (t-test) in +/- Elemental Weight Percent (Average of Sample):
ELEM: Ca Si
60ci .025 .029
80ci .039 .046
90ci .051 .060
95ci .063 .073
99ci .088 .103
Test of Homogeneity (t-test) at 1.0 % Precision (Average of Sample):
ELEM: Ca Si
60ci yes yes
80ci yes yes
90ci yes yes
95ci yes yes
99ci yes yes
Level of Homogeneity (t-test) in +/- Percent (Average of Sample):
ELEM: Ca Si
60ci .1 .1
80ci .1 .2
90ci .1 .2
95ci .2 .3
99ci .3 .4
Range of Ideal Homogeneity (t-test) in +/- Elemental Weight Percent (Average of Sample) (Meisenkothen and Donovan):
ELEM: Ca Si
60ci .071 .030
80ci .110 .047
90ci .144 .062
95ci .176 .075
99ci .247 .106
Range of Actual Homogeneity (t-test) in +/- Elemental Weight Percent (Average of Sample) (Meisenkothen and Donovan):
ELEM: Ca Si
60ci .091 .106
80ci .141 .164
90ci .186 .216
95ci .227 .264
99ci .318 .370
Here are the trace elements, so you can see it is very clean:
Un 3 Wollastonsite (Willsboro,NY)
TakeOff = 40.0 KiloVolt = 20.0 Beam Current = 100. Beam Size = 20
(Magnification (analytical) = 24000), Beam Mode = Analog Spot
(Magnification (default) = 600, Magnification (imaging) = 100)
Image Shift (X,Y): .00, .00
Number of Data Lines: 10 Number of 'Good' Data Lines: 10
First/Last Date-Time: 10/02/2007 10:17:11 PM to 10/03/2007 04:34:37 AM
WARNING- Using Exponential Off-Peak correction for ti ka
WARNING- Using Average Off-Peak correction for al ka
WARNING- Using Alternating On and Off Peak Acquisition
Average Total Oxygen: 41.377 Average Total Weight%: 100.000
Average Calculated Oxygen: 41.377 Average Atomic Number: 13.577
Average Excess Oxygen: .000 Average Atomic Weight: 23.214
Average ZAF Iteration: 2.00 Average Quant Iterate: 2.00
Oxygen Calculated by Cation Stoichiometry and Included in the Matrix Correction
Element Si is Calculated by Difference from 100%
Un 3 Wollastonsite (Willsboro,NY), Results in Elemental Weight Percents
ELEM: Ti Fe Al Mn Mg Si Ca O
TYPE: ANAL ANAL ANAL ANAL ANAL DIFF SPEC CALC
BGDS: EXP LIN AVG LIN LIN
TIME: 1200.00 1200.00 1200.00 1200.00 1200.00
BEAM: 100.09 100.09 100.09 100.09 100.09
ELEM: Ti Fe Al Mn Mg Si Ca O SUM
135 n.d. .018 .001 .011 .023 24.286 34.280 41.380 100.000
136 .001 .018 n.d. .010 .030 24.282 34.280 41.379 100.000
137 .001 .020 .002 .013 .0322 24.275 34.280 41.376 100.000
138 .002 .022 n.d. .010 .0346 24.275 34.280 41.376 100.000
139 .001 .021 .0005 .011 .0336 24.276 34.280 41.377 100.000
140 .001 .022 .0007 .010 .0328 24.276 34.280 41.376 100.000
141 .0007 .027 .0007 .012 .019 24.283 34.280 41.377 100.000
142 .002 .020 n.d. .012 .0363 24.274 34.280 41.376 100.000
143 .001 .021 .0007 .012 .0371 24.272 34.280 41.375 100.000
144 .002 .021 n.d. .012 .0375 24.272 34.280 41.375 100.000
AVER: .001 .021 .0006 .011 .0316 24.277 34.280 41.377 100.0
SDEV: .001 .002 .001 .001 .006 .005 .000 .002 .000
SERR: .000 .001 .000 .000 .002 .002 .000 .000
%RSD: 43.729 11.747 90.602 9.035 19.207 .020 .000 .004
STDS: 22 395 336 140 12 0 0 0
STKF: .5616 .6862 .1159 .4052 .4215 .0000 .0000 .0000
STCT: 56847.7 30610.4 9737.5 4924.6 29326.9 .0 .0 .0
UNKF: .0000 .0002 .0000 .0001 .0002 .0000 .0000 .0000
UNCT: 1.0 7.9 .3 1.1 11.7 .0 .0 .0
UNBG: 92.2 42.8 38.5 9.4 21.1 .0 .0 .0
ZCOR: 1.2726 1.1868 1.5126 1.2198 1.8866 .0000 .0000 .0000
KRAW: .000 .000 .000 .000 .000 .000 .000 .000
PKBG: 1.011 1.186 1.009 1.121 1.553 .000 .000 .000
Detection limit at 99 % Confidence in Elemental Weight Percent (Single Line):
ELEM: Ti Fe Al Mn Mg
135 .001 .001 .001 .001 .001
136 .001 .001 .001 .001 .001
137 .001 .001 .001 .001 .001
138 .001 .001 .001 .001 .001
139 .001 .001 .001 .001 .001
140 .001 .001 .001 .001 .001
141 .001 .001 .001 .001 .001
142 .001 .001 .001 .001 .001
143 .001 .001 .001 .001 .001
144 .001 .001 .001 .001 .001
AVER: .001 .001 .001 .001 .001
SDEV: .000 .000 .000 .000 .000
SERR: .000 .000 .000 .000 .000
Percent Analytical Relative Error (One Sigma, Single Line):
ELEM: Ti Fe Al Mn Mg
135 -752.7 2.2 21.7 6.4 1.3
136 20.6 2.2 -74.9 6.9 1.0
137 19.5 2.0 14.8 5.4 1.0
138 14.6 1.9 58.7 6.8 .9
139 19.5 2.0 46.1 6.7 .9
140 18.1 1.8 35.0 7.0 1.0
141 38.6 1.5 35.6 6.1 1.6
142 15.9 2.0 118.8 5.8 .9
143 20.8 1.9 34.3 5.8 .9
144 16.0 1.9 86.3 5.9 .9
AVER: -56.9 1.9 37.6 6.3 1.0
SDEV: 244.6 .2 50.5 .6 .2
SERR: 77.3 .1 16.0 .2 .1
Detection Limit (t-test) in Elemental Weight Percent (Average of Sample):
ELEM: Ti Fe Al Mn Mg
60ci .000 .001 .000 .000 .002
80ci .000 .001 .000 .000 .003
90ci .000 .002 .000 .001 .004
95ci .000 .002 .000 .001 .005
99ci .001 .003 .001 .001 .007
Analytical Sensitivity (t-test) in Elemental Weight Percent (Average of Sample):
ELEM: Ti Fe Al Mn Mg
60ci .000 .000 --- .000 .001
80ci .000 .000 --- .000 .001
90ci .000 .000 --- .000 .002
95ci .000 .000 --- .000 .002
99ci .000 .001 --- .000 .003
We have a lot of clean material so just ask if you need some.
Minerals from Ward's are of two types, hand samples and research mineral samples. They are chosen for their relatively large size and euhedral morphology. There is no information about their chemical composition and really nothing can be assumed about their homogeneity.
An ideal microanalysis standard is free, has large grains, is homogeneous on both a micron and macro scale, and has been characterized by a method in addition to EPMA.
Most materials being considered for EPMA standards fail one or more of these criteria, usually homogeneity is the problem.
The Smithsonian Microbeam Standards are a far superior set of materials because they have been hand picked to identify clean grains, mounted and sigma ratio measured to assess intragrain and intergrain homogeneity, and analyzed by wet chemistry. Some of them are only available as small grains.
The wollastonite that John discusses is probably the best case material. It contains trace/minor Fe, Mn, etc. which is typical of many wollastonites (the crystal structure does not welcome more than trace concentrations of Mg, Fe, etc. compared to the augite and orthopyroxene structures). It may be a decent standard but it really requires a major effort to characterize the material that would be selected for distribution as a standard.
I would expect that the hornblende, like Kakanui hornblende, contains inclusions. That is the reality of natural minerals. That presents a real problem in stating what the composition "is" and issues regarding use of that material as a potential standard.
I support exploration of these materials. The ideal set of calibration materials for the geology community is end-member, stoichiometric, homogeneous materials available in large chunks. For example, I use Elba hematite as our primary Fe standard but always include secondary Fe standards in the PFE run. This Elba hematite is probably from the Caltech mineral collection, is not an internationally recognized EPMA standard, but is Fe-rich and homogeneous. The Smithsonian magnetite is an equivalent standard and could be used (the Smithsonian ilmenite is good but contains some inclusions of hematite and other phases). The Rockport fayalite standard likely contains grunerite and magnetite in the mineral separate used for the SMS wet chemical analysis, so it is decent material but the accepted analysis is faulty; this can only be corrected by cleaning the separate and reanalyzing the bulk material.
So the ideal standard setup is to have materials that have the highest element concentration expected in a probe run, but avoiding problem materials (Quartz: beam sensitive, Si peak shift vs. most minerals(?), Corundum: conductivity issues, peak shift, and so on). The accuracy of the calibration is then demonstrated by analysis of accepted standards such as the SMS materials (we use Kakanui hornblende).
The Ward's wollastonite could be a usable standard but I recall seeing BSE zoning in the large pieces. This ultimately, like many materials, disqualifies it because when you crush it for distribution, you have many grains with variation in the chemistry. When a user mounts up 1-2 grains they implicitly assume those grains are the true composition when they probably aren't. This issue is a problem for the commercial standard mounts but notice that they mostly contain end member phases like Sb2S3 which are stoichiometric and homogeneous.
The SMS are free to anyone who requests them. There is material from a larger size fraction that can be requested but that is not necessarily what was used for the wet chemistry, and especially for Kakanui hornblende, the larger fraction has grains with larger inclusion of ilmenite, etc. So there is no easy answer (except synthetic glasses, which I can elaborate on).
Cheers,
Paul
Quote from: Paul Carpenter on December 18, 2014, 08:45:17 AM
Minerals from Ward's are of two types, hand samples and research mineral samples. They are chosen for their relatively large size and euhedral morphology. There is no information about their chemical composition and really nothing can be assumed about their homogeneity.
Hi Paul,
I respectfully disagree. Homogeneity can be demonstrated by purity in many cases.
If one has crystalline SiO2 that is 99.99% pure, then the bulk chemistry is homogenous by definition. The same is true for pure elements, pure oxides, many pure sulfides and some simple compounds (though not all).
The Ward's wollastonite is homogeneous because it is extremely pure with just a few traces. Even if the trace elements varied by a considerable amount, the bulk chemistry would not change significantly because their contribution to the bulk chemistry is so insignificant.
And in fact, we have measured many individual grains and the trace chemistry, in the splits that we have, are all within the trace element precisions. So there is nothing that can contribute to variation in the bulk chemistry. Therefore it makes an excellent standard for Ca and Si and possibly oxygen as well.
And even if there were some tiny inclusions of another mineral, well then, because we *did not* average them into the bulk chemistry by using wet chemistry, we can simply avoid those inclusions in the EPMA and have the exact composition that pure CaSiO3 *must* have.
Quote from: Paul Carpenter on December 18, 2014, 08:45:17 AM
An ideal microanalysis standard is free [sic], has large grains, is homogeneous on both a micron and macro scale, and has been characterized by a method in addition to EPMA.
Most materials being considered for EPMA standards fail one or more of these criteria, usually homogeneity is the problem.
The Smithsonian Microbeam Standards are a far superior set of materials because they have been hand picked to identify clean grains, mounted and sigma ratio measured to assess intragrain and intergrain homogeneity, and analyzed by wet chemistry. Some of them are only available as small grains.
By this criteria, at least a few of the Smithsonian standards (e.g., Kakanui hornblende) are far from superior as demonstrated by investigators (Vicenzi, Fournelle, etc) who have shown the presence of many inclusions that were averaged into the bulk wet chemistry. Hand picked grains are great, but because the "hand picker" cannot see *into* each grain, they cannot know how many inclusions exist inside each grain. See this post for evidence of this:
http://smf.probesoftware.com/index.php?topic=216.msg1499#msg1499
Quote from: Paul Carpenter on December 18, 2014, 08:45:17 AM
The Ward's wollastonite could be a usable standard but I recall seeing BSE zoning in the large pieces.
I'd like to see evidence for this claim. Even if this wollastonite varied in trace elements (and they do not so far as we have determined), how could that trace element variation affect the bulk average atomic number of CaSiO3 which is the BSE signal? You may have been seeing electron channeling effects... which are quite common even in pure (crystalline) materials.
Quote from: Paul Carpenter on December 18, 2014, 08:45:17 AM
This issue is a problem for the commercial standard mounts but notice that they mostly contain end member phases like Sb2S3 which are stoichiometric and homogeneous.
Which is exactly the case for this particular Ward's wollastonite! You are welcome to any amount of this cleaned material for further investigation in your lab.
Quote from: Owen Neill on September 12, 2018, 08:42:24 PM
Necroing an old thread here, but I went looking for the Willsboro, NY wollastonite, and while Ward's don't sell it as a standard anymore, I was able to buy some in bulk. There are calcite inclusions to work around, but the wollastonite itself is a fairly promising Ca standard. Also, since I bought in bulk, I now have ~1kg of material, which is about 0.99kg more than I'll ever need. If you want some, contact me off-line.
Apparently, great minds think alike... ;)
I bought this material from Ward's about 15 years ago, crushed it and have a large supply of grains. And yes, it's very pure, a good standard material, just by assuming stoichiometry.
I'll try and find my trace element analyses of it and post them.
john
I found the trace data on the Ward's Willsboro wollastonite. It appears I did this analysis 11 years ago:
Un 3 Wollastonsite (Willsboro,NY)
TakeOff = 40.0 KiloVolt = 20.0 Beam Current = 100. Beam Size = 20
(Magnification (analytical) = 24000), Beam Mode = Analog Spot
(Magnification (default) = 600, Magnification (imaging) = 100)
Image Shift (X,Y): .00, .00
Formula Based on Sum of Cations = 8.00 Oxygen Calc. by Stoichiometry
Number of Data Lines: 10 Number of 'Good' Data Lines: 10
First/Last Date-Time: 10/02/2007 10:17:11 PM to 10/03/2007 04:34:37 AM
WARNING- Using Exponential Off-Peak correction for ti ka
WARNING- Using Average Off-Peak correction for al ka
WARNING- Using Alternating On and Off Peak Acquisition
Average Total Oxygen: 60.613 Average Total Weight%: 100.000
Average Calculated Oxygen: 19.293 Average Atomic Number: 12.437
Average Excess Oxygen: 41.320 Average Atomic Weight: 20.735
Average ZAF Iteration: 2.00 Average Quant Iterate: 2.00
Oxygen Calculated by Cation Stoichiometry and Included in the Matrix Correction
Oxygen Calculated by Cation Stoichiometry Also Includes 41.320 Oxygen as a Specified Concentration
Element Si is Calculated by Difference from 100%
Un 3 Wollastonsite (Willsboro,NY), Results in Elemental Weight Percents
ELEM: Ti Fe Al Mn Mg Si Ca O
TYPE: ANAL ANAL ANAL ANAL ANAL DIFF SPEC CALC
BGDS: EXP LIN AVG LIN LIN
TIME: 1200.00 1200.00 1200.00 1200.00 1200.00 --- --- ---
BEAM: 100.09 100.09 100.09 100.09 100.09 --- --- ---
ELEM: Ti Fe Al Mn Mg Si Ca O SUM
135 .000 .018 .001 .011 .026 4.824 34.502 60.617 100.000
136 .001 .019 .000 .010 .034 4.819 34.502 60.615 100.000
137 .001 .020 .002 .013 .036 4.812 34.502 60.612 100.000
138 .002 .022 .000 .010 .039 4.812 34.502 60.612 100.000
139 .001 .021 .001 .011 .038 4.813 34.502 60.613 100.000
140 .001 .022 .001 .010 .037 4.813 34.502 60.613 100.000
141 .001 .027 .001 .012 .021 4.822 34.502 60.614 100.000
142 .002 .020 .000 .012 .041 4.810 34.502 60.612 100.000
143 .001 .021 .001 .012 .042 4.809 34.502 60.611 100.000
144 .002 .021 .000 .012 .042 4.809 34.502 60.611 100.000
AVER: .001 .021 .001 .011 .036 4.814 34.502 60.613 100.000
SDEV: .001 .002 .001 .001 .007 .005 .000 .002 .000
SERR: .000 .001 .000 .000 .002 .002 .000 .001
%RSD: 43.73 11.75 90.60 9.04 19.21 .11 .00 .00
STDS: 22 395 336 140 12 --- --- ---
STKF: .5616 .6862 .1160 .4052 .4215 --- --- ---
STCT: 56847.7 30610.4 9737.5 4924.6 29326.9 --- --- ---
UNKF: .0000 .0002 .0000 .0001 .0002 --- --- ---
UNCT: 1.0 7.9 .3 1.1 11.7 --- --- ---
UNBG: 92.2 42.8 38.5 9.4 21.1 --- --- ---
ZCOR: 1.2627 1.1927 1.6722 1.2235 2.1256 --- --- ---
KRAW: .0000 .0003 .0000 .0002 .0004 --- --- ---
PKBG: 1.01 1.19 1.01 1.12 1.55 --- --- ---
Detection limit at 99 % Confidence in Elemental Weight Percent (Single Line):
ELEM: Ti Fe Al Mn Mg
135 .001 .001 .001 .001 .001
136 .001 .001 .001 .001 .001
137 .001 .001 .001 .001 .001
138 .001 .001 .001 .001 .001
139 .001 .001 .001 .001 .001
140 .001 .001 .001 .001 .001
141 .001 .001 .001 .001 .001
142 .001 .001 .001 .001 .001
143 .001 .001 .001 .001 .001
144 .001 .001 .001 .001 .001
AVER: .001 .001 .001 .001 .001
SDEV: .000 .000 .000 .000 .000
SERR: .000 .000 .000 .000 .000
Percent Analytical Relative Error (One Sigma, Single Line):
ELEM: Ti Fe Al Mn Mg
135 -752.7 2.2 21.7 6.4 1.3
136 20.6 2.2 -74.9 6.9 1.0
137 19.5 2.0 14.8 5.4 1.0
138 14.6 1.9 58.7 6.8 .9
139 19.5 2.0 46.1 6.7 .9
140 18.1 1.8 35.0 7.0 1.0
141 38.6 1.5 35.6 6.1 1.6
142 15.9 2.0 118.8 5.8 .9
143 20.8 1.9 34.3 5.8 .9
144 16.0 1.9 86.3 5.9 .9
Hi all
I can also confirm I have not seen any BSE zoning in Willsboro wollastonite. I acquired a number of samples off ebay earlier this year for U-Pb garnet dating and had a look at a number of chips on the SEM prior to analysis. It appeared to be quite homogeneous on BSE at least.
Cheers
We use Gates wollastonite, obtained from Mike Shaffer when he ran the University of Oregon lab. It is an excellent standard but is an in-house secondary standard and I am not aware of any other lab using the material. Many wollastonites contain variable levels of elements such as Mg, Mn, and Fe (2+ cation substitution), and since it is a metamorphic mineral, there can be inclusions of calcite, grossular, diopside, and other skarn phases.
The real issue is that if material from Ward's or from the Smithsonian mineral collection is to be used as an EPMA standard, it needs to be screened for intra and inter-grain homogeneity, observed to be free of inclusions, and if possible analyzed by a technique besides the electron microprobe. Many of us comment on the homogeneity but it is based on the few grains we received or mounted up for analysis. The method used by Jarosewich was to mount up ~100 grains at a larger size fraction than the distributed material. The sigma ratio data supplied with the SMS data sheet summarizes the best and worst grain variations from analyses on that mount.
A given hand sample-sized piece is typical of the Smithsonian material, so there is nothing special with the exception that all distributed material comes from that exact master sample, and is therefore "traceable" in that sense. It is therefore important to distribute from that sample that was characterized. If people also purchase from Ward's the same material, there is no control on whether that sample really is equivalent to that bought by the person that did the initial screening.
So I agree with John that the wollastonite has great potential. I think if we continue this dialog with Tim Rose at the Smithsonian, we could make progress on EPMA standards.
Cheers,
Paul
Quote from: Paul Carpenter on September 24, 2018, 12:42:52 PM
We use Gates wollastonite, obtained from Mike Shaffer when he ran the University of Oregon lab. It is an excellent standard but is an in-house secondary standard and I am not aware of any other lab using the material. Many wollastonites contain variable levels of elements such as Mg, Mn, and Fe (2+ cation substitution), and since it is a metamorphic mineral, there can be inclusions of calcite, grossular, diopside, and other skarn phases.
The real issue is that if material from Ward's or from the Smithsonian mineral collection is to be used as an EPMA standard, it needs to be screened for intra and inter-grain homogeneity, observed to be free of inclusions, and if possible analyzed by a technique besides the electron microprobe. Many of us comment on the homogeneity but it is based on the few grains we received or mounted up for analysis. The method used by Jarosewich was to mount up ~100 grains at a larger size fraction than the distributed material. The sigma ratio data supplied with the SMS data sheet summarizes the best and worst grain variations from analyses on that mount.
A given hand sample-sized piece is typical of the Smithsonian material, so there is nothing special with the exception that all distributed material comes from that exact master sample, and is therefore "traceable" in that sense. It is therefore important to distribute from that sample that was characterized. If people also purchase from Ward's the same material, there is no control on whether that sample really is equivalent to that bought by the person that did the initial screening.
So I agree with John that the wollastonite has great potential. I think if we continue this dialog with Tim Rose at the Smithsonian, we could make progress on EPMA standards.
I would be more than pleased to send the Smithsonian my Ward's Science wollastonite material. I have a large hand specimen and a vial of crushed and somewhat separated material.
Just FYI, I had a chat with an emeritus professor a long time ago who pointed out to me that it's pronounced *wo*llastonite, not wo*llas*tonite, because that's how the dude's name was pronounced. I had not known that!
john