These perfectly spherical ejecta are possibly accretionary lapilli which have been altered to gypsum by acid volcanic vapours at Solfatara
Teodoro Monticelli (1759-1846), while Professor of Chemistry at the University of Naples (appointed in 1808), developed a keen interest in rocks and minerals and soon amassed a collection of some 2,000 to 3,000 specimens. When it became known that Monticelli wished to dispose of his collection Humphrey Davy acted as the mediator with the Trustees of the British Museum and on 26 May 1823 the first consignment of five boxes arrived. A further eight boxes arrived a few months later and Monticelli was paid the then considerable sum of £510 in total.
The first attempt at recording the Monticelli Collection fell to Charles Konig (the first curator at the Museum to specialise in rocks and minerals) who worked until January 1825. Konig died in 1851 and the collection was not touched until Thomas Davies (1862-92) continued work 60 years later. The final cataloguing was done by Frederick Bannister, a Cambridge physicist, who was appointed to the Department in 1927.
Above: Map of the area from which Monticelli collected his samples
This specimen is an example of a dark grey trachyte lava. It has been dated literally by being pressed into an inscribed mould while still molten. The inscription translates as 'Alliance... Of Thunder and Liberty... Sealed with the burning lava of Vesuvius… March 1820... by... C. Gimbernat'
At present the Collection comprises 423 minerals and 346 rocks, the latter making up the Monticelli Rock Collection. Konig made reference to 'duplicates' and it could be that the removal of these reduced the size of the holding. The Rock Collection is registered with the numbers BM68180-68204, BM68217-68245 and BM68251-68542. Eight of these are from Mt Vulture, with the remainder from the Mt Vesuvius region including Monte Somma, Campi Phlegraei, Naples, Pozzuoli, the islands of Procida and Ischia, Pompeii, Torre del Greco and Sarno.
All the rocks are the product of volcanic eruptions, the dolomites of BM68534 and BM68541 occurring as blocks within agglomerates. Tuff, lapilli tuff, pumice, ash and sand make up 33% of the collection. BM68400 is an example of Pozzolana, the porous pumice-rich tuff used by the Romans to make cement.
Trachyte, leucitophyre and undifferentiated lava comprises 26, 20 and 5% of the 346 rocks. Many of these were collected from flows dated from A.D. 79 and from 23 separate occasions between 1734 and 1823, and this is an unusual feature of this collection.
Vuggy 'mica-pyroxene bomb' containing the mineral vesuvianite (BM68520) The 25% vug spaces up to 20 mm across have been lined with a well-crystallised black-brown mica. Polished versions of rock similar to this also occur in the Hamilton Collection
Many of Monticelli's sample areas overlapped with those of Sir William Hamilton and therefore the Monticelli Collection can sometimes put the rocks of the Hamilton Collection into a more natural perspective. One example of this is specimen BM68520. Registered as 'mica-pyroxene bomb' from Monte Somma, this specimen is of a very strongly altered rock with a buff-coloured vuggy matrix, which could have once been a dolomite. It also contains vesuvianite.
For further information contact: David Smith
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