No. I. — Account of Mount Vesuvius. 211 



merates of the bay as to the more recent operations of the vol- 

 cano. The rarity of this mineral is interesting in an archaelo- 

 gical view ; and I have given some account of it in my Essay 

 on the Building Materials used by the Romans in the last No. 

 of this Journal, p. 38, &c. 



Of the genus chrysolite, we find in Vesuvius the olivine or 

 volcanic chrysolite in great perfection. Its colour is pale and 

 yellowish green, and it is generally found massive in volcanic 

 rocks, or in grains ejected from the crater. I have seen a fine 

 specimen beautifully crystallized in a four-sided prism, with 

 the angles truncated, forming additional sides. Of the garnet, 

 Vesuvius produces several varieties. The most important is the 

 idocrase, or Vesuvian, — a beautiful mineral, generally imbedded 

 in calcareous rocks, and of a colour between brown and green. 

 The form of its crystals varies extremely. The maximum num- 

 ber of sides, according to Haiiy, is not less than ninety. See 

 also Fig. 96, Vol. ii. of Molls' Mineralogy by Haidinger. It 

 commonly occurs in some modification of the four-sided prism, 

 frequently with four smaller truncating planes, and the termi- 

 nations variously bevelled and acuminated. The lustre is vitre- 

 ous, frequently approaching resinous, and the sides of the 

 prisms are streaked longitudinally. Though the pyramidal 

 garnets of Vesuvius are the most esteemed, they are found in 

 other parts of Europe in primitive mountains, especially at 

 Arendal in Norway. Among the other varieties of garnet, the 

 melanite is the most important; its form is usually the rhom- 

 boidal dodecahedron ; and it is of a fine velvet black colour. 

 It is found in the calcareous rocks of Monte Somma ; but its 

 most important locality is at Albano and Frescati, near Rome. 

 It is probable that the colophonite or resinous garnet also oc- 

 curs at Vesuvius. The common garnet occurs very generally 

 massive, and of various colours in this volcano. 



Of the metals we have little to say. I have already noticed 

 the remarkable occurrence of gold chemically detected in the 

 volcanic sand of 1822, and have mentioned a green salt of 

 copper in its proper place. Probably the only substance which 

 occurs under the external metallic character in Vesuvius is 

 iron. The specular iron ore is here found in great beauty. We 

 have it in small and splendent concretions superimposed on tra- 



