134 



The mineral has a very high adamantine lustre. Under 

 the orthoscope the lorenzenite prisms always show extinction 

 parallel to their longitudinal direction, on whatever faces they 

 may be placed. A section oriented parallel to the first pinacoid 

 is nearly colourless. Only a faint brownish tinge is observable. 

 The light vibrating parallel to the ß-axis is transmitted without 

 any perceptible absorption. The light vibrating parallel to the 

 &-axis, on the other hand, is somewhat more absorbed. The 

 axial colour is faintly brownish inclining to violet. A section 

 oriented parallel to the second pinacoid is somewhat more 

 deeply coloured than the foregoing. Also here the light that 

 vibrates parallel to the c-axis is transmitted without any per- 

 ceptible absorption. The light vibrating parallel to the «-axis 

 is most strongly absorbed, and the axial colour is the same 

 here as parallel to the 6 -axis, though somewhat more intense. 

 The absorption of light referred to the crystallographical axes 

 is thus , 



In sections parallel to the second pinacoid the axial image 

 about the first mean line appears under the conoscope. The 

 plane of the optic axes is parallel to the first pinacoid. 

 The direction of the greatest velocity of light (the index a) 

 coincides with the c-axis, the medium velocity of light (the 

 index ß) coincides with the a -axis, and the least velocity (the 

 index Y) with the è-axis. As the last-mentioned direction is at 

 the same time the first mean line (the acute bisectrix), lorenzenite 

 consequently is optically positive. 



The single crystals are too small to furnish material for 

 prisms for determining the indices of refraction. IVor is it pos- 

 sible to produce a section perpendicular to the second mean 

 line for the usual measurement of the angle between the optic 

 axes. The optical constants could not, therefore, be fully 

 determined. 



