getting tired of going in circles
Aug. 3rd, 2008 08:50 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
kareinaSo far today I've put in 8 hours of uni work. The first two went beautifully--I created a figure, and it all went smoothly, and turned out to be beautiful as well as informative. Alas, it is a figure which goes with things I'd written yesterday, so no new words have appeared in the thesis for that.
Then I started what was meant to be productive work, but hasn't yet resulted in any new words for the thesis. The sample I'm currently writing up is one I'd not gotten the "garnet fractionation path" calculations to work for previously, so I thought I'd try the manual subtraction technique I've used a couple of times with some success. But this time, rather than just subtracting the amount of garnet that is predicted to be present at the conditions I'd calculated for the garnet core, I decided that it would be more appropriate to subtract an amount which actually corresponds with how much of my sample I think is garnet core. Sounded nice and straightforward. Alas, I have determined that I simply don't know how to do such a calculation.
I set up an Excel spreadsheet to do the actual calculations for me, and each of the formulas I've entered does what I think it is doing, I've checked that over, and over again. This part of the spreadsheet takes the predicted amount of each of the minerals and the ingredients that make up each mineral (MnO, FeO, etc...) and calculates the same wt% as the program predicted. All good.
The next part takes the amount of garnet I *really* think is there and adjusts the total wt% of the rock to show that since there is more garnet than had been predicted, there is less of everything else. This part seems to work fine--if I change it to a higher number for how much garnet I think is there, the totals increase garnet and decrease everything else. If I tell it that there is less garnet, the totals change the other way.
The next part I've tried two different ways. The first attempt I multiplied the amount of each ingredient for each mineral by the ratio of the predicted amount of the mineral, with the amount that would be there as a result of the change in amount of garnet. This results in totals that change if I change the amount of garnet back in step two. The second attempt did more or less the same thing, but actually calculated the change to the number of mols of each mineral if there is more or less garnet. It also results in numbers which change when I change the amount of garnet.
From there I've added up the totals for each ingredient from each mineral (this much FeO in the garnet, plus this much in biotite, etc.) to get totals for each ingredient, and subtracted the garnet (I also tried just adding them up without the garnet--gives the same number, as it should).
The final step is where I'm running into problems. Since the program I'm going to give the numbers to do the calculations as to what minerals are stable at what temperatures and pressures needs the input in terms of weight percent (wt%), and percent are out of 100, I've been "normalizing" them, by adding up the totals, then dividing each ingredient by the total, to get a percentage.
However, it turns out that when you do this, it does not matter how much garnet you subtract--it can be 1% or 90%, while everything else in the spreadsheet changes in response to that change, the "normalized" row always gives the same numbers.
This can't be correct--if the rock is 50% garnet and that garnet is not available for reactions then the "effective bulk composition" of everything else *must* be different than if the rock is 5% garnet and that 5% that isn't available for reactions. Therefore I am doing something wrong here. But I've been looking at it too long, and simply can't see where I'm going wrong. If any of you have enough of a background in chemistry or enough basic logic skills to tell me what I'm doing wrong and how to fix it, let me know. Heck, I would even be willing to e-mail you the spreadsheet,if you think it would help...
In the mean time I'd best go write up a sample description for one of the other samples, so that there will be some new words for today. Sigh.
Then I started what was meant to be productive work, but hasn't yet resulted in any new words for the thesis. The sample I'm currently writing up is one I'd not gotten the "garnet fractionation path" calculations to work for previously, so I thought I'd try the manual subtraction technique I've used a couple of times with some success. But this time, rather than just subtracting the amount of garnet that is predicted to be present at the conditions I'd calculated for the garnet core, I decided that it would be more appropriate to subtract an amount which actually corresponds with how much of my sample I think is garnet core. Sounded nice and straightforward. Alas, I have determined that I simply don't know how to do such a calculation.
I set up an Excel spreadsheet to do the actual calculations for me, and each of the formulas I've entered does what I think it is doing, I've checked that over, and over again. This part of the spreadsheet takes the predicted amount of each of the minerals and the ingredients that make up each mineral (MnO, FeO, etc...) and calculates the same wt% as the program predicted. All good.
The next part takes the amount of garnet I *really* think is there and adjusts the total wt% of the rock to show that since there is more garnet than had been predicted, there is less of everything else. This part seems to work fine--if I change it to a higher number for how much garnet I think is there, the totals increase garnet and decrease everything else. If I tell it that there is less garnet, the totals change the other way.
The next part I've tried two different ways. The first attempt I multiplied the amount of each ingredient for each mineral by the ratio of the predicted amount of the mineral, with the amount that would be there as a result of the change in amount of garnet. This results in totals that change if I change the amount of garnet back in step two. The second attempt did more or less the same thing, but actually calculated the change to the number of mols of each mineral if there is more or less garnet. It also results in numbers which change when I change the amount of garnet.
From there I've added up the totals for each ingredient from each mineral (this much FeO in the garnet, plus this much in biotite, etc.) to get totals for each ingredient, and subtracted the garnet (I also tried just adding them up without the garnet--gives the same number, as it should).
The final step is where I'm running into problems. Since the program I'm going to give the numbers to do the calculations as to what minerals are stable at what temperatures and pressures needs the input in terms of weight percent (wt%), and percent are out of 100, I've been "normalizing" them, by adding up the totals, then dividing each ingredient by the total, to get a percentage.
However, it turns out that when you do this, it does not matter how much garnet you subtract--it can be 1% or 90%, while everything else in the spreadsheet changes in response to that change, the "normalized" row always gives the same numbers.
This can't be correct--if the rock is 50% garnet and that garnet is not available for reactions then the "effective bulk composition" of everything else *must* be different than if the rock is 5% garnet and that 5% that isn't available for reactions. Therefore I am doing something wrong here. But I've been looking at it too long, and simply can't see where I'm going wrong. If any of you have enough of a background in chemistry or enough basic logic skills to tell me what I'm doing wrong and how to fix it, let me know. Heck, I would even be willing to e-mail you the spreadsheet,if you think it would help...
In the mean time I'd best go write up a sample description for one of the other samples, so that there will be some new words for today. Sigh.
![[identity profile]](https://www.dreamwidth.org/img/silk/identity/openid.png){kind=small}
(no subject)
Date: 2008-08-03 01:29 pm (UTC)Are the changes in bulk composition so small that they don't show up if your spreadsheet shows two or three decimal places?
(no subject)
Date: 2008-08-03 09:54 pm (UTC)Thanks for taking the time to look at the question! Hope you had a good hike. Its a lovely morning here, I should try to make time for a hike during daylight hours myself, after dart they are more on the order of "strolls"...