Julie,
In our experience, oxide standards are poor choices for light
elements in unknowns with relatively high atomic numbers. We would
use an almandine standard for Fe, Al, Si; a rhodonite for Mn,
synthetic geikielite for Mg, synthetic pyrophanite for Mn, the
wollastonite may be OK if it is coarse enough. I think the problem
lies with some or all of the light elements, Mg, Al, Si, where the Z
and A corrections will be very large with these standards. Penn St.
Univ. does have a good garnet standard (Ingamells almandine). I
think that using FeSiO3 would also be good for Si, but you still need
a high Z standard for Al and Mg. By the way, SiO2 is easily beam
damaged if you use a point beam with currents greater than 10 nA.
eric
>Hi Eric
>
>We are heavily dependent on pure oxide standards for most of our work:
>I've been using:
>
>SiO2 (synthetic)
>Al2O3 (synthetic)
>Fe2O3 (synthetic
>MnO (synthetic)
>MgO (synthetic)
>Wollastonite (synthetic)
>
>Operating conditions:
>I normally run the probe with the accelerating voltage at 15 kV.
>I've tried juggling the sample current, everywhere from about 12 na
>to 6 na. That hasn't seemed to solve anything.
>
>If by getting in a couple of different garnet standards I could get
>around the analytical problems I am encountering, I would be really
>pleased if you could/would offer some suggestions...
>
>Thanks, Julie Vry
>
>
>
>P.S. I don't have any garnet standards in the minerals bar, just:
>olivine (San Carlos, USNM 111312/444; Springwater meteorite, USNM 2566);
>augite (Kakanui, New Zealand)
>pyroxene (P.S.U. Px-1, Goldich et al. Can J. Earth Sci 4, 747, 1967)
>Diopside (P.S.U. 63-1827)
>Amphibole, Engels
>Hornblende (P.S.U. 4-190)
>Tremolite
>Grunerite
>Biotite (P.S.U. 5-110)
>Biotite (U.M. R-2208)
>Albite, Amelia Ab-1
>Orthoclase Or-1
>Ilmenite, Ilmen Mtns (USNM 96189)
>Gahnite (Brazil) (USNM 145883)
>Obsidian, comenditic, KN18, Naivasha, Kenya
>Basaltic glass, VG-A99, Makaopuhi, Hawaii (USNM 113498/1)
>Rhyolitic glass, VG-568, Yellowstone Nat. Park (USNM 72854)
>
>>Julie,
>> What standards are you using and what operating conditions when
>>you get 103 wt%?
>>eric
>>
>>>I encounter persistent difficulties in analysing the Fe-Ca-Mn garnets
>>>(about 1/3 of each component) that are common on the NZ Southern Alps
>>>(usually I get about 103% totals). I suspect that the problem is in
>>>the matrix correction factors, but that is not easy for me to sort
>>>out.
>>>
>>>I wonder if using a garnet standard of similar composition might help...
>>>(I don't have such a standard)
>>>
>>>Any suggestions as to how I might deal with the problem would be
>>>appreciated.
>>>The probe (a 20+ year-old JEOL JXA-733 SuperProbe, using Moran
>>>Scientific software) works wonderfully except for this.
>>>
>>>Julie Vry
>>>--
>>>Dr. Julie Vry
>>>Senior Lecturer - Geology (metamorphic petrology)
>>>School of Earth Sciences
>>>Victoria University
>>>PO Box 600
>>>Wellington, New Zealand
>>>
>>>
>>>
>>>phone, office: 64 4 463 6432 (please do NOT leave messages here)
>>>please leave messages at: 025 644 5598
>>>fax 64 4 463 5186
>>>email: [log in to unmask]
>
>--
>Dr. Julie Vry
>Senior Lecturer - Geology (metamorphic petrology)
>School of Earth Sciences
>Victoria University
>PO Box 600
>Wellington, New Zealand
>
>
>
>phone, office: 64 4 463 6432 (please do NOT leave messages here)
>please leave messages at: 025 644 5598
>fax 64 4 463 5186
>email: [log in to unmask]
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