Corsi Collection of Decorative Stones

view of stone 852

Corsi 852, approx. 145 x 73 x 40 mm, © Oxford University Museum of Natural History

OUMNH Number: 852  
Name and quarry location: Granito bigio grafico, from Fontaine du Gènie, Tipaza, Algeria; or just possibly syenite della Balma, from Balma Biallese, Biella, Lombardy, Italy  
Geological description: Medium to fine-grained syenite of predominantly plagioclase feldspar, beige-coloured potash feldspar, biotite, muscovite and black hornblende.  
Comments: This stone appears to be, like no.818, granito bigio grafico described by both Mielsch (1985) and Borghini (1997) who say that it comes from Tipaza, in Algeria, where there are many examples of its use. A sample is in the Peschetto Collection in Rome labelled 'Granito grafico, porfido grigio micaceo' from Ancient Rome (Mausoleum of Augustus). However others have said that it is the Balma syentite (sienite della Balma) which has been quarried in the Val Cervo, near the town of Balma Biallese, in Italy, since the 19th century. It is of Oligocene age. Cardu (2004) describes the quarrying of this stone and cites many examples of its use. Because Corsi included it among his ancient stones, the Algerian provenance is the more likely.  
References: Borghini (1997) 218; Cardu et al., in Prikryl (2004) 289-294; Corsi (1845) 210-211, 218-219; Mielsch (1985) 69, taf.23. Other examples: Servizio Geologico d'Italia, Rome, Pescetto Coll.137.  
Further information:

Corsi's classification: Class 16. Granites; ii. Italian granites  
Corsi's text: 209.4 Granito delle Alpi  

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