Hey's Mineral Index is a standard reference work in mineralogy. It is an alphabetical index of known mineral species and varieties and includes synonyms. For species and major varieties it provides more detailed entries. The work also contains a classification of minerals based on their chemistry into 32 top-level groups, with each group broken down further.
Its value lies in combining two functions in one volume: name retrieval and chemical classification. A reader can locate an entry quickly through a mineral name or synonym, or browse related mineral families by chemical composition. This arrangement made it a long-standing desk reference in museums, universities and exploration laboratories.
The main body is an alphabetical list of mineral and variety names. Each entry typically gives the mineral name, chemical formula or composition, principal occurrence and diagnostic features, and, under species entries, notes on varieties and synonyms. Major varieties are often listed separately so that they can be distinguished from the species itself.
The chemical classification assigns minerals to 32 top-level groups. These groups broadly follow the chemical character of the anion or anionic group, including native elements, sulfides, oxides, halides, carbonates, sulfates, phosphates and silicates, and are further divided by cation combinations and structural relationships. The classification emphasises chemical affinity, making it easy to compare minerals with similar compositions and modes of occurrence.
Compared with structure-driven schemes, a chemical classification directly serves identification and compositional analysis: when a chemical analysis is available, the candidate list can be narrowed quickly, while the alphabetical index leads readers from an old or alternative name back to the relevant chemical group. The two entry points complement each other and are central to the book's continued use.
The succession of editions reflects the growth of mineralogy. New mineral species are continually approved by the International Mineralogical Association, old names and synonyms require cleaning, and chemical classifications must be adjusted as analytical techniques improve. The third edition became a standard citation in many laboratories during the 1990s, and the delay and cancellation of the fourth edition left it as the practical authority for many years.
Several classification systems coexist in mineralogy. The Dana classification is based on chemical composition and structural relationships, uses a detailed numbering system and is widely used in mineral databases. The Strunz classification, now usually called Nickel-Strunz, is organised around chemical formulae and structures, divides minerals into ten major classes and is recommended by the International Mineralogical Association. Hey's 32 top-level groups are closer to traditional chemical grouping, with more groups and finer subdivisions, and are suited to rapid retrieval by chemical composition.
The systems are not mutually exclusive. Dana and Strunz provide systematic numbers and hierarchies, while Hey's index provides names, synonyms and a chemical-group cross-reference. Researchers often cite both a Strunz number and a Hey's entry so that readers can approach a mineral from different directions.
To use the index, a reader normally looks up a mineral name or synonym in the alphabetical section, then follows the chemical formula into the appropriate chemical group and compares the composition and properties of related minerals. For varieties, the index notes the relationship to the parent species, which helps prevent a variety from being mistaken for an independent mineral species.
The main limitation is the date of publication. Mineralogy is a growing field, new species are approved every year, and old names and synonyms are revised. A printed index cannot reflect these changes in real time. Modern practice therefore combines Hey's index with the IMA official mineral list, the Mindat database, the RRUFF spectral database and the Handbook of Mineralogy to obtain current species status, locality and crystallographic data.
The index is primarily organised by English names, so Chinese readers need a Chinese-English mineral-name concordance. Entry counts and classification details may also differ between editions. Citations should therefore specify the edition and publication year rather than mixing content from different versions.
Hey's Mineral Index is commonly found in geological libraries, museums and university mineralogy departments. The first and second editions, because of their age, are studied as documents in the history of mineralogy and scientific publishing, while the third edition remains a common second-hand and library item because of its wide use. Citations normally give the title, edition and year to distinguish it from other mineral indexes.