Introduction: hemimorphite is a secondary mineral species found typically in the oxidized zone of zinc-bearing mineral deposits. During the eighteenth century this mineral was grouped with other secondary zinc species including smithsonite and hydrozincite under the name calamine. This has caused considerable problems when reviewing old literature particularly as the term was still being used well into the nineteenth century.

Occurrence in Wales: hemimorphite was, during the eighteenth century grouped with other secondary zinc species including smithsonite and hydrozincite under the name calamine. This causes considerable problems when reviewing old literature particularly as the term was still being used well into the nineteenth century. In 1848, W.W. Smyth described the presence of hemimorphite in Central Wales, ‘Calamine, the siliceous species, has occurred in considerable quantity at Nant y Creiau mine, below the adit level, but has been thrown away as a worthless “spar”: elsewhere it may be seen investing blende with a thin crust’. Only by the use of the term ‘siliceous species’ can the true identity of this ‘calamine’ be made – smithsonite and hydrozincite both being carbonates. Prior to this, Sowerby (1817) illustrated, white botryoidal silical oxide of zinc from North Wales. The description is certainly of hemimorphite and although no more accurate locality information is given, the specimen is likely to have been derived from Flintshire. Although hemimorphite was clearly known about, the earliest specimen of hemimorphite in the National Museum of Wales collections dates from 1927. G.J. Williams, the former H.M. Mine Inspector for North Wales had in his collection a sample from Devil’s Bridge, displaying finely crystalline spherical hemimorphite crystal aggregates encrusting quartz crystals overgrowing sphalerite veinstone. No new discoveries were made then, until, in the late 1960s mineral collectors began to take an interest in the minerals of the Central Wales Orefield. A number of new localities were found along with the rediscovery of G.J. Williams’ original site. In South Wales, quarrying of the Carboniferous Limestone during the 1980s and 90s resulted in the discovery of the some of the finest Welsh hemimorphite specimens, particularly at Machen Quarry, near Caerphilly. Hemimorphite occurs here within barite-galena veins cutting dolomitic limestone. Many of the veins had been worked at one time for the lead ore, therefore, it is not suprising that hemimorphite has also been found at a number of disused mine sites within the same area.

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