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Major element chemistry is determined by atomic absorption and emission spectroscopy using the fluoboric-boric acid method of Bernas (1968) and Buckley and Cranston (1971). Fe²⁺ is determined by the modified Wilson (1955) cold acid dissolution method.

Sample preparation: Rock and mineral samples are prepared for chemical analysis by first crushing the material in a jaw crusher and then a rotary pulverizer with ceramic plates (Figs. 1 & 2). The resulting powder is split to about a 20 gram sample using a microsplitter (Fig. 3). The split is then reduced to fine powder by manual grinding with a ceramic mortar and pestle.

Figure 1. Rotary pulverizer.	Figure 2. Student pouring sample into rotary pulverizer.
Figure 3. Splitting sample.

Sample Dissolution: Samples are dissolved in a teflon cup in a Parr bomb (Figs. 4 & 5). 100 mg of sample is placed in the teflon cup along with 1 ml nitric acid and 10 ml hydrofluoric acid. The bomb is heated for 2 hours at 120^oC. After cooling the product is transferred to a beaker containing a boric acid solution and the mixture is stirred until a perfect solution is achieved.

Figure 4. Teflon cup and disassembled Paar acid digestion bomb.

Figure 5. Assembled Paar acid digestion bomb.

Atomic Absorption and Emission Analysis: The chemical composition of individual samples is determined by comparing the intensity of absorption and emission lines to that of solutions of known concentration. Na and K are done by atomic emission and Fe, Mn, Ca, and Mg are determined by atomic absorption using an air-acetylene flame (Fig. 6). Because of their more refractory character, Si, Al, and Ti are determined by atomic absorption using a nitrous oxide-acetylene flame (Fig. 7).

Figure 6. Student aspirating solution into the atomic absorption/emission spectrometer.

Figure 7. Nitrous oxide-acetylene flame used for analyzing the refractory elements Si, Al, and Ti.

References:

Bernas, B. (1968). A new method for decomposition and comprehensive analysis of silicates by atomic absorption spectrometry. Analytical Chemistry 40, 1682-1686.

Buckley, D. E. and Cranston, R. E. (1971) Atomic absorption analysis of 18 elements from a single decomposition of aluminosilicate. Chemical Geology 7, 273-284.

Wilson, A. D. (1955) A new method for the determination of ferrous iron in rocks and minerals. Bulletin of the Geological Survey of Great Britain 9, 56-58.

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