SPI Supplies Individual Mounted Microanalysis Standard Item, Minerals Group, Obsidian
This is a reflected light micrograph of a polished, carbon coated obsidian grain. The identifying etched label, which is a feature of our standards, is invaluable for navigating in an electron beam instrument. 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 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.
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