5. Obsidian Na,K,Al,Fe silicate glass
Obsidian is a volcanic glass containing the full range of
rock-forming elements from hydrogen to iron. Because of its glassy state,
the alkali elements Na and K are not tightly bound and, like other glasses
in this set, may therefore migrate giving instability in intense electron
bombardment. However, the composition
has been well established through repeated analysis by classes of students,
it is a most useful standard for general use in silicate analysis.
Locality unknown; University of Alberta #5831>
| Element | % |
| Oxide | % |
|---|
| H | 0.09 | | H2O | 0.80 |
| O | 48.63 | | | |
| F | 0.07 | | F | 0.07 |
| Na | 3.01 | | Na2O | 4.06 |
| Mg | 0.04 | | MgO | 0.07 |
| Al | 6.94 | | Al2O3 | 13.11 |
| Si | 34.56 | | SiO2 | 73.94 |
| Cl | 0.36 | | Cl | 0.36 |
| K | 4.18 | | K2O | 5.04 |
| Ca | 0.54 | | CaO | 0.76 |
| Ti | 0.06 | | TiO2 | 0.10 |
| Mn | 0.05 | | MnO | 0.06 |
| Fe | 1.34 | | FeO | 1.72 |
|
|
|
| Sum | 99.9 | | Sum | 100.1 |
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