208 Physical Notices on the Bay of Naples. 



sures of lavas, covering them with a peculiar green crust. It is 

 most abundant in the lavas of 1804 and 1805. My specimen 

 is from that of 1820, at the cratere del Francese ; it is a mu- 

 riate of copper. Mica is an abundant production of Vesu- 

 vius, and varies considerably in its appearance. Sometimes it 

 is black and thickly slaty, like that in the lava of the extinct 

 volcano of Albano; at other times bright-greenish, with a sil- 

 very lustre. Its form is the six-sided prism, or in tables. 



Among the zeolites, by far the most famous is the leucite, 

 known also under the name of the white garnet of Vesuvius. 

 This remarkable and beautiful mineral has twenty-four trape- 

 zoidal faces when fully crystallized. Its specific gravity, ac- 

 cording to Brisson, is 2.4684 ; its hardness 5.5 — 6.0. They 

 are very seldom transparent, generally translucent, and of a 

 grayish white colour. They vary greatly in size. The largest 

 known is in the Edinburgh Museum, from Thompson's collec- 

 tion, and measures 1.64 inches along the greater axis, and 

 1.23 the smaller. Sometimes they are so small as to require 

 a lens for their inspection. They abound amazingly in some 

 lavas, as I have already remarked. When much injured by 

 heat, as often happens, they are called leocita cotta, or baked 

 leucite. It is found in greatest perfection in a rather vesicu- 

 lar lava of no great hardness, but tough, in that part of the 

 mountain named La Ilia Cupa di Sobotionella. It contains 

 potash in remarkable quantity. The following are the results* 

 of four analyses ; the first three by Klaproth, the last by Vau- 

 quelin. 



Silica, 

 Alumina, 

 Potassa, 

 Lime, 



Though not confined to Vesuvius, this mineral seems pe- 

 culiar to Italy, at least as far as authentic information goes. 

 I have before me specimens from its three principal localities, 

 Vesuvius, the lava at Capo di Bove near Rome, and the ex- 

 tinct volcanic formations near Radicofani in Tuscany. Of the 



* Taken from Breislak's Campanie, vol. ii. p. 4, and Allan's Mineralo* 

 gical Analyses. 



