Eric's ideal formula for lithosite, K6Al4Si8O25.2H2O, gives acceptable
structural formulae and back-calculated wt% H2O for Dr. Liu's analyses, with
~0.2 vacancies [] among the 18 cationic sites:
Analyses (wt %):
1 2 3 avg
SiO2 45.40 47.24 46.90 46.51
TiO2 0.23 0.14 0.22 0.19
Al2O3 20.17 20.39 21.16 20.57
FeO 0.00 0.00 0.00 0.00
MnO 0.00 0.00 0.00 0.00
MgO 2.53 2.65 2.54 2.57
CaO 0.17 0.07 0.07 0.10
Na2O 0.13 0.12 0.12 0.12
K2O 24.80 24.81 24.58 24.73
Cr2O3 0.05 0.06 0.05 0.05
H2O 3.52 3.61 3.62 3.58
------ ------ ------ ------
96.98 99.08 99.25 98.42
Structural formulae:
Si 7.735 7.834 7.753 7.775 \
Al(4) 0.265 0.166 0.247 0.225 /8.000
Al(6) 3.784 3.818 3.874 3.827 \
Cr 0.007 0.008 0.006 0.007 |
Ti 0.030 0.017 0.027 0.024 |
Mg 0.179 0.157 0.093 0.142 /4.000
Mg 0.462 0.498 0.533 0.498 \
Ca 0.030 0.012 0.013 0.018 |
Na 0.043 0.039 0.037 0.039 |
K 5.389 5.248 5.183 5.273 |
[] 0.077 0.203 0.234 0.172 /6.000
O 25.000 25.000 25.000 25.000
H2O 2.000 2.000 2.000 2.000
Accordingly, let's forget my hypothetical "new mineral", K4Al3Si6O16(OH)5!
But the reaction relationship among lithosite, muscovite, quartz and
Kfeldspar is no less intriguing:
K6Al4Si8O25.2H2O + KAl2AlSi3O10(OH)2 + 10 SiO2 = 7 KAlSi3O8 + 3 H2O
How commonly has lithosite been misidentified as "white mica" in high P/T
chlorite-zone rocks that lack Kfeldspar?
Dugald
Dugald M Carmichael Phone/V-mail: 613-533-6182
Dept of Geological Sciences and Geological Engineering
Queen's University FAX: 613-533-6592
Kingston ON K7L3N6 E-mail: [log in to unmask]
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