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  • Print publication year: 2012
  • Online publication date: November 2012

Chapter 3 - How are minerals identified?

Summary

Identification of minerals in hand specimens is the main emphasis of this chapter. The methods used are careful visual evaluation and basic tests with easily available tools. Only at the end of this chapter do we briefly introduce some sophisticated instrumental methods that are used in the quantitative characterization of minerals and other crystalline solids. Chapter 6 is devoted to the study of minerals with a polarizing optical microscope.

The identification of an unknown mineral in a hand specimen begins with making observations that allow us to assess a specimen’s overall form (or crystal habit if it is well crystallized), state of aggregation, and color. Those properties that allow us to identify a mineral or at least narrow down the possibilities are said to be diagnostic. Color is probably the first property the observer sees, followed by the overall shape of the mineral. But, though instantly noted, color is not a reliable diagnostic property in most minerals, because many (chemically variable) mineral groups exhibit a range of colors.

Important physical properties that characterize a mineral and allow us to separate one from another in hand specimens are the following:

Habit

State of aggregation

Color

Luster

Cleavage

Hardness

Specific gravity (or relative density)

Each of these properties is discussed in this chapter, but it must be recognized that the actual process of mineral identification is best learned in the laboratory part of the course you are enrolled in. There you will tune your observational skills through the study of labeled mineral specimens as well as unknowns. Here, we first introduce those properties that can be evaluated by observation only – habit, state of aggregation, color, and cleavage – and subsequently discuss properties such as hardness, specific gravity, magnetism, radioactivity, and solubility in hydrochloric acid, all of which require testing tools.

FURTHER READING
Bose, S.Hochella, M. F.Gorby, Y. A.Kennedy, D. W.McCready, D. E.Madden, A. S.Lower, B. H. 2009 Bioreduction of Hematite Nanoparticles by the Dissimilatory Iron Reducing BacteriumShewanella Oneidensis MR-1. Geochemica et Cosmochimica Acta 73 962
Darragh, P. J.Gaskin, P. J.Sanders, J. V. 1976 OpalsScientific American 234 84
Dyar, M. D.Gunter, M. E.Tasa, D. 2008 Mineralogy and Optical MineralogyMineralogical Society of AmericaChantilly, VA
Goldstein, J.Newbury, D.Joy, D.Lyman, C.Echlin, P.Lifshin, E.Sawyer, L.Michael, J. 2003 Scanning Electron Microscopy and X-Ray MicroanalysisKluwer Academic/Plenum PublishingNew York
Jenkins, R.Snyder, R. L. 1996 Introduction to X-Ray Powder DiffractometryJohn Wiley and SonsNew York
Klein, C. 2008 Minerals and Rocks: Exercises in Crystal and Mineral Chemistry, X-Ray Powder Diffraction, Mineral and Rock Identification, and Ore MineralogyJohn Wiley and SonsNew York
Klein, C.Dutrow, B. 2008 Manual of Mineral ScienceJohn Wiley and SonsNew York
Loeffler, B. J.Burns, R. G. 1976 Shedding light on the color of gems and mineralsAmerican Scientist 64 636
Mineral Magnetism: From Microbes to Meteorites 2009 Elements 5 209
Nassau, K. 1978 The Origin of Color in MineralsAmerican Mineralogist 63 219
Nassau, K. 1980 The Causes of ColorScientific American 243 124
Perkins, D. 2011 MineralogyPrentice HallUpper Saddle River, NJ
Wenk, H. R.Bulakh, , A. 2004 Minerals: Their Constitution and OriginCambridge University Press, Cambridge
Williams, D. B.Carter, C. B. 1996 Transmission Electron MicroscopyPlenum PressNew York