SPI Minerals Group

	Element	%		Oxide	%		obsidian
	H	0.09		H2O	0.80				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. Locality unknown; U. of Alberta #5831
	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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Name	Description	SPI #	Each
Obsidian	SPI SuppliesŪ Individual Mounted Microanalysis Standard Item	AS1250-AB	$199.56