210 Physical Notices on the Bay of' Naples. 



mixed with rocks and volcanic materials, but its proper appear- 

 ance is not altered. Breislak says, that the iron pyrites are 

 never seen in the lazulite of Vesuvius. His remarks are, how- 

 ever, chiefly applied to the substance I was next going to name, 

 which, though much allied in appearance to this mineral, has 

 not yet been referred to its place in the physiographic system ; 

 I mean the Hauyne. This beautiful blue mineral is found in 

 great perfection at Vesuvius, which is one of its few localities.* 

 Its colour may, I think, be most correctly stated at smalt-blue. 

 In this it differs from the fine azure-blue of the lazulite. 



Of the order Gem, we have several important genera. The 

 spinel ruby has been ejected from the crater in considerable 

 quantity, especially in 1794. Its variety, the ceylanite, is 

 found very perfectly crystallized in the Monte Somma. The 

 form of both is the simple octohedron, sometimes beautifully 

 truncated on the angles, and with other occasional differences. 



Topaz occurs, but in very minute crystals, in Monte Somma, 

 as also, I believe, the schorlite or schorlous topaz. Several 

 varieties of rhomboidal quartz of course occur. Of these 

 chalcedony is the principal ; and, on the whole, quartz cannot 

 be considered as an abundant production of Vesuvius. Under 

 the species of fusible quartz we have the obsidian and pumice. 

 The former is extremely scarce, and is hardly considered a 

 Vesuvian mineral. I have, however, two curious specimens 

 of it. In one from the old crater of Monte Somma, the 

 obsidian, of a beautiful velvet black, and a high degre of lustre, 

 is contained in ovoidal cavities of a leucitic lava ; the other is 

 of so late production as October 1822. Pumice is another un- 

 common production of the volcano, and it seems to belong, if 

 I do not mistake, wholly to those masses ejected by the erup- 

 tions of the Monte Somma. My specimen I found among 

 such fragments in the Fossa Grande. Breislak asserts f that 

 near Castelamare he found much pumice, which must have 

 come at a former period from Mount Vesuvius, of the thick- 

 ness of two or three feet. As far as the account goes, how- 

 ever, it may as well belong to the ancient pumiceous conglo- 



* It occurs also in the extinct volcanos near Rome, and on the banks of 

 the Rhine. 

 t Vol. i. p. 26. 



