Natural Minerals Group

From the standards library of SPI Supplies and the C. M. Taylor Company

# AS1250-AB


Na,K,Al,Fe silicate glass

ElementWt % OxideWt %
H 0.09H2O 0.80
O 48.63
F 0.07F 0.07
Na 3.01Na2O 4.06
Mg 0.04MgO 0.07
Al 6.94Al2O3 13.11
Si 34.56SiO2 73.94
Cl 0.36Cl 0.36
K 4.18K2O 5.04
Ca 0.54CaO 0.76
Ti 0.06TiO2 0.10
Mn 0.05MnO 0.06
Fe 1.34FeO 1.72

Sum 99.9 Sum100.1

Loose pieces
note conchoidal glassy fracture surfaces

Polished obsidian
U. of Alberta #5831
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.

Name Description SPI # Each
Obsidian SPI SuppliesŪ Individual Mounted Microanalysis Standard Item AS1250-AB $
Obsidian SPI SuppliesŪ Individual Loose Microanalysis Standard Item AS1255-AB $

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