﻿Geology and Natural History. 163 



side of this lake; but great fissures were opened widely, and the 

 small lake of Rotomahana was converted into an area of geysers 

 and cinder craters, a dozen or more having been suddenly put 

 into action, the geysers throwing up water and mud, and the cra- 

 ters steam and stones and clouds of ashes. Mt. Tarawera is 

 known to have consisted of volcanic rocks, but not as a volcano, 

 or as containing a crater. Its summit was a sacred place with 

 the natives where no foreigner was permitted to intrude. The 

 eruptions from the Mt. Tarawera region as far as reported were 

 of stones and ashes, nothing being yet known as to ejected lavas. 

 The ashes have buried deeply the country around, destroy- 

 ing the village of Waroa and others beyond recovery, and caus- 

 ing the death of more than a hundred persons, among whom were 

 some English settlers. The region of the eruption is comprised 

 within the large geyser area of New Zealand, which extended 

 from that of Tarawera and Rotorua southwest to Mt. Tongariro. 

 A good map of it and an account of the geysers is contained in 

 Dr. Peale's Report on Geysers, Hay den's Geol. Survey, for 1878, 

 and republished in 1883, at p. 313. 



3. New Minerals. — Professor A. Weisbach has recently pub- 

 lished a description of the interesting new mineral, called by him 

 Argyrodite, in which the new element Germanium has been dis- 

 covered (this Journal, xxxi, 308). Argyrodite crystallizes in the 

 monoclinic system ; the crystals are small and often united in 

 rounded groups, so that they do not allow of exact measurement. 

 The prominent planes are the prism with an angle of 115°, a clino- 

 dome {\-ls\\-l=- 120°) and a negative hemipyramid ( — 1-f/s, — 

 1-§=130°); the axial relation deduced is d:b:c (vertical) = 

 1 : 1*67 : 0*92. Twin crystals and drillings are common, united so 

 that the vertical axes are inclined 112° to each other. The physi- 

 cal characters are : hardness=2*5 ; specific gravity = 6'093 — 6*111; 

 luster metallic; color steel-gray with a tinge of red on the fresh 

 fracture, tarnishing on exposure; streak grayish black, shining; 

 no cleavage, rather brittle. An analysis by Winkler afforded : 

 S Ge Ag Fe Zn 



17-13 6-93 74-72 0'66 0-22=99'66 



Argyrodite occurs as a crust upon marcasite and siderite, or again 

 on argentite ; other associated minerals are sphalerite, galena 3 py- 

 rite and chalcopyrite, and also the silver minerals pyrargyrite, 

 polybasite and stephanite. The locality is the Himmelfurst mine 

 near Freiberg. 



Arminite is another new name given by Weisbach to a hydrous 

 sulphate of copper found on porcelain-jasper from Planitz, near 

 Zwickau, where it has been formed in the course of the burning 

 of a bed of coal. It forms a green coating resolved by the micro- 

 scope into short needles or scales. The material analyzed was 

 scanty and more or less impure; the analysis, regarded as the 

 most reliable, gave Winkler : 



S0 3 CuO Fe 2 3 , Al a 3 CaO 



24-43 56-81 0'35 0'56 = 82-15 



Am. Jour. Scl— Third Series, Vol. XXXII, No. 188— August, 1886. 

 10a 



