4 
Jounston-Lavis—The Hruption of Vesuvius in April, 1906. 197 
I avoid laying any stress upon the differences of the amphiboles (hornblende) 
and nephelines, for mineralogists have not yet settled upon the characters that 
define the many different species of these mineral families. 
One of the drusic minerals is leucite. Whether this required a higher 
temperature, the absence of fluorides, chlorides, or sulphates in the vapour 
from which it was deposited is an interesting problem. That it is not an abyssal 
mineral I demonstrated many years ago, and M. Lacroix has re-discovered this 
fact.* Accidental minerals enclosed in the few pieces of pumices, pumiceous 
scoriz, and scoriz examined by him are referred to as essential constituents. 
The future student of Vesuvius will be met by a vast amount of casual uncorre- 
lated notes on different ejecta, made all the more complicated by a profuse and 
unnecessary nomenclature. 
The third class of ejecta may be classed as fumarolized rocks, in which true 
surface fumarolic minerals have been deposited, and in which the volcanic vapours 
have acted in a more or less destructive manner on the rock constituents. ‘These 
blocks and their contents obviously come from no great depth, and are quite 
similar to those so frequently met with quite at the surface. In some blocks we 
have to deal with agglomerates and breccias, and in other larger pieces of older 
lavas and dyke rock. 
Furthermore, we can separate them into those only slightly altered and 
reddened, and those highly fumarolized and converted into red, orange, or light 
yellow masses. It was in two blocks of slightly altered, reddened scoria that the 
cavities were found lined with halite and sylvite in beautiful cubes up to a centi- 
metre or more in diameter. Associated with this was a new mineral, which I have 
described,t and which has subsequently been studied crystallographically by 
Mr. L. J. Spencer. ‘This mineral, which I have called chlormanganokalite, is a 
double chloride of potash and manganese, as results from the following analysis made 
in May, 1907, on nearly a gram of material, which gave the following results :— 
K : . 86°34 or KCl 5 : 09242 
Win, 5 5 JIL MnCl, . 6 . 26°45 
Gh =. ; . 48:13 MgCl, . ; . 0-16 
Mg . ; . 0:04 Na,SO,. ; 5. leit) 
Na . , . 0°38 BO) ; . 1°52 
SO, . ; . O81 Insoluble : ee Oeil 
HOM : 5 LG —- 
Insoluble : 5 M7 99:45 
99°45 
* T cannot help thinking that M. Lacroix has not given sufficient attention to the literature of 
Vesuvyian eruptions, including papers by Prof. Scacchi and myself; nor are his specimens always adequately 
localized or their field relations recorded. 
+ Nature, May 31st, 1906, vol. lxxiv., pp. 103, 104; and Johnston-Lavis and L. J. Spencer, ‘On 
