50 Scientific Proceedings, Royal Dublin Society. 



become luminous here and there over their surface. This, I ascer- 

 tained, was due to the fragments of orthoclase adhering to the 

 hexagons. Mr. Moss has been aware of this peculiarity of the 

 Dublin orthoclase for many years, having, like myself, discovered 

 it accidentally. 



2. Radiating Beryl. 



This second type differs from the first in habit only, but this 

 habit is one not noticed in the descriptive mineralogies, and 

 evidently, at any rate, developed in the crystals found at Grlen- 

 cullen to a rare degree of perfection. 



The crystals radiate in the most regular and striking manner, 

 not alone fanwise, but as cones or sphere segments. The pris- 

 matic form seems fully preserved in the individual crystals, but 

 each crystal is tapered, dwindling at last to the common centre of 

 radiation. For some distance around this centre no structure, other 

 than radiating lines, is indeed noticeable : further out the crystals 

 individualize, and their prismatic form is apparent. If a chip 

 from near the centre of one of these cones is placed between crossed 

 nicols it is found to extinguish parallel to the radiating lines ; hence, 

 the fact that the axis of the prism lies along these lines is almost 

 assured. 



A section taken through the centre of a small group of radiat- 

 ing crystals revealed strongly-marked cleavage along the radii, a 

 cleavage at right angles to this also well marked, and faint cleav- 

 age lines intersecting at about 100°, this angle being external to 

 the centre, and bisected by the radii. Countless enclosures, mostly 

 vitreous, are present, generally elongated along the radius ; these 

 are very minute. 



These radiating beryls are pale-green, bluish-green, yellow, 

 and yellow-brown; translucent to opaque, when they are often 

 quite white in colour. Sometimes they are highly altered when 

 they fall under the third type, where they will be described. 

 Basal cleavage cracks cross the radii in lines roughly circular 

 round the centre of radiation. The crystals easily break along 

 this cleavage, producing a stepped appearance along the radii. 



The groups are all more or less fan-like in section, that is, the 

 cone seems never to merge into the sphere ; they are occasionally 



