Corsi Collection of Decorative Stones

view of stone 822

Corsi 822, approx. 145 x 73 x 40 mm, © Oxford University Museum of Natural History

OUMNH Number: 822  
Name and quarry location: Granito della Sedia di San Pietro, from Wadi Umm Wikala, near Wadi Semna, Eastern Desert. Egypt  
Geological description: Gabbro or metagabbro (weakly metamorphosed) with some alteration of the green augite to brown?  
Comments: Nos. 821 and 822 are samples of granito della Sedia di San Pietro, the stone that was used for the inlays in the plinth of the bronze stature of a seated St Peter in St Peter's Basilica in the Vatican. It has also been called ofite because it was thought to come from Mons Ophyates (Wadi Semna). Others have suggested the name comes from 'ophytes' meaning snake, because it was used in Hellenistic times for amulets to ward of the effects of snake bites, a superstition that persisted in Roman times. Granito della Sedia di San Pietro is actually from Precambrian basement rocks at Wadi Umm Wikala.  
References: Borghini (1997) 234-235; Corsi (1845) 210-211, 217-218; Harrell (2010a); Lazzarini (2002c) 237-238; Mielsch (1985) 69, taf.24; Price (2007) 231  
Further information:

Corsi's classification: Class 16. Granites; i. Antique granite  
Corsi's text: 205.10 Granito antico. Marmor Syenite. Marmo Sienite... [trovata] presso la città di Siene sul confine fra Egitto, e l'Etiopia... Pyrrhopoecilon... Psaronion...Aethiopicum perchè... era Siene sul confine dell' Etiopia. Altra specie [Granito della Sedia].  

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