Author: Rob Lavinsky
Content by courtesy of : The Arkenstone www.irocks.com
Reproduction of text and photos prohibited without permission of author.
Using Emission Spectroscopy to examine chemical element spectra generated in an electric arc one can identify (or rule out) key elements in minerals. Actual examples have been to distinguish with certainty between Australian Wulfenite and Stolzite by identifying the molybdenum or tungsten spectral lines. Other examples: pink Chinese morganite or apatite? in this case the chemical phosphate test gave an unequivocal answer. Banded white smithsonite or something looking like it? (Result: strong response to zinc and carbonate). We use a combination of methods because no method is complete.
When you can define your ID problem in terms of the presence or absence of a key element or chemical moeity we can probably help.
X-ray powder can identify on the order of 95% of all minerals. Minerals which cannot be distinguished are species with identical structures and similar sized ions. For example, siegenite and violarite have nearly exactly the same cell parameter (+/- 0.01 A) and thus cannot be distinguished by X-ray.
Powder work requires approximately a 2 mm cube of material.
RAMAN spectroscopy has the advantage of being completely nondestructive, but only a few hundred minerals have published patterns. For example, this is useful for identifying a perfect gem crystal since you will not damage the crystal at all in the sampling.