November 30, 2020, 02:08:37 AM
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Topic: Need Help With A Little Geochemistry Problem  (Read 160 times)

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Offline HelloScience

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Need Help With A Little Geochemistry Problem
« on: November 07, 2020, 07:49:22 PM »
Hello, I need to see what others think about this situation.

I have a material said to be basalt. I have been given major element data in ppm and would l like to use the percentages of corresponding oxides moving forward. Here is the deal:

Al2O3 is 16.31% in the ball park. Given Al at 43,152.08 ppm.
Fe2O3 is 10.15% in the ball park.  Given Fe at 41,625.02 ppm.
SiO2 is 1.41%. Given Si at 4,498.08 ppm.

[(Element ppm)(Oxide mass/Element mass)/(10,000)] = % Oxide

Is this correct? Any ideas what this material might be?

Thank you,
Andrew H.

Offline AWK

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Re: Need Help With A Little Geochemistry Problem
« Reply #1 on: November 08, 2020, 01:51:11 AM »
If you look at Wikipedia, you can read that the SiO2 content in basalt is in the range of 45-52%. The Si content of SiO2 is about 47% (for the estimate, I assume a value of 50% with an error of less than 10%). This means that you should expect a Si content in the basalt of ~250,000 ppm. Well, under no circumstances can the name basalt be used for your sample.

As for your strange calculations - with the Si content of around 4,500 ppm ("Given Si at 4,498.08 ppm.") and Si to O2 mass ratio of 28:32 (which is slightly less than 50% for silicon content) the percentage of SiO2 in your sample will be slightly less than 0.9%. Your quoted percentages of Al2O3 and Fe2O3 in the basalt are plausible but by no means correspond to the Al and Fe content in ppm in your sample.
AWK

Offline HelloScience

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Re: Need Help With A Little Geochemistry Problem
« Reply #2 on: November 08, 2020, 02:00:59 AM »
Thanks, I see the error in my calculations now.

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