Mineral classification

There are several schemes of mineral classification in common use, usually derived from published guides to mineralogy. The International Mineralogical Association (IMA), which governs mineral nomenclature through its Commission on New Minerals, Nomenclature and Classification (CNMNC), has also proposed the outlines of a unified scheme but, as of December 2009, the details have yet to be finalised: it seems likely that it will be a modified version of the Strunz classification.

The IMA-CNMNC has proposed the following hierarchy for class names. Some of the existing systems use slightly different terminology.

• Mineral class.
  • Mineral subclass.
    • Mineral family.
      • Mineral supergroup.
        • Mineral group.
          • Mineral subgroup or mineral series.

A mineral group is defined by the IMA-CNMNC as consisting of "two or more minerals with the same or essentially the same structure, and composed of chemically similar elements."

Strunz classification

The Strunz classification was developed by German mineralogist K. Hugo Strunz (1910–2006) in his Mineralogische Tabellen (1941), as an update of the original Dana classification. The then-available Dana classification dated from 1895, and took no account of the discoveries that had been made into mineral structure through X-ray crystallography.

The Strunz tables have been regularly updated, and the last published edition is the ninth (2001). The eighth and ninth editions were cowritten with Australian mineralogist Ernest H. Nickel (died 18 July 2009), and the system is sometimes referred to as Nickel–Strunz classification.

A tenth version of the classification has been developed, but not formally published: it differs only slightly from the version in the ninth edition of the Strunz Mineralogical Tables, mostly by separating out borate minerals into a class of their own, separate from carbonates and nitrates. The new version, sometimes referred to as "Strunz 10", is currently used by the IMA and by many mineralogical databases.

The "Strunz 10" classification is based on ten mineral classes, determined by the chemical identity of the anion and identified by a two-digit number. There are two intermediate levels of classification, identified by capital letters, above the mineral group or mineral series, which is idnetified by a two-digit number. The Strunz classification number of a mineral need not be unique to that mineral, although in practice it often is.

Dana classification

The original Dana classification is the earliest systematic classification of minerals, introduced by the pioneering American mineralogist James Dwight Dana (1813–95) in his System of Mineralogy (1837). This original classification became somewhat dated with the time lapse between new editions of the book: the sixth edition (edited by Dana's son, Edward) was published in 1895, while the seventh did not appear until 1944 and the eighth (as Dana's New Minerology) in 1997.

The classification in Dana's New Minerology is slightly different from that which went before it, as it has no fewer that 78 "classes", most of which would be subclasses in other classification systems. Nevertheless, it preserves the concept based on anion composition and structural elements, and all of the new Dana "classes" can be seen as subclasses of the old ones.

Below the "classes" are mineral "types" and mineral "groups", each indicated by a two-digit numbers separated by full points. Finally, within each group, each mineral species is assigned a fourth two-digit number: hence (unlike other classification systems), each mineral is individually numerically identified. Dana classification numbers do, however, change from time to time due to reclassification.

Hey's Chemical Index of Minerals

A third classification system was introduced by British mineralogist Max H. Hey (1904–84) in his An Index of Mineral Species and Varieties Arranged Chemically, with an Alphabetical Index of Accepted Mineral Names and Synonym (1950, better known as the Chemical Index of Minerals or simply the Hey Index), and is currently on its third edition (1993). Hey's system is more centered on the chemical properties of minerals that on structural features.

Hey was assistant keeper in the Department of Mineralogy of the British Museum (Natural History) in London. As with the Strunz classification, Hey's system arose from the insufficiencies of the 1895 Dana classification and the desire to reorganize a large mineral collection along systematic lines. It is said that it was inspired by a query from the public (in 1942) as to how many different types of magnesium silicate were known in nature, and the amount of work needed to find the answer. Originally intended as an internal index for the Natural History Museum, it was published in 1950 and was very influential in British mineralogy.

Hey's classification is based on 38 "primary groups", with a single level of classification below that. Silicates of magnesium, for example, form group 14.4 (ten members). As such, it is a coarser classification than the Strunz or new Dana systems.

External links

• Strunz classification (complete listing)
• Dana classification (complete listing)
• Hey's Chemical Index of Minerals (primary groups)