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XXI.— ON THE OCCUKKENCE OF HAEMOTOME AT GLEN- 

 DALOUGH, CO. WICKLOW. By J. JOLY, B.E., Assistant to 

 the Professor of Civil Engineering, Trinity College, Dublin. 



[Bead, April 21, 1886.] 



As I can find no previous mention of the occurrence of harmotome, 

 or indeed of any member of the zeolite family of minerals, in Co. 

 Wicklow, it may not be amiss to call attention to its presence. I 

 have the more excuse for writing a note on the occurrence oi this 

 one mineral, as, since the work of Daubre, a special geological and 

 mineralogical interest is attached to the beautiful group of which 

 it is a member. 1 



The harmotome of Glendalough occurs in the out-put from the 

 Luganure lode, which traverses the granite close to its junction 

 with the schist, and extends into the vale of Grlendasan. Much of 

 the gangue has been thrown out at the upper end of the lake, and 

 from this debris I took, some few years ago, a very small specimen 

 of the zeolite— so small that I could not be assured of its identity 

 as harmotome till I was so fortunate recently as to find another 

 and larger specimen. The out-put otherwise indicates hydro-ther- 

 mal action in the lamellar deposits of quartz and calcite. Here 

 also may be found fluorite, sphalerite, barite, strontianite, galenite, 

 pyrite, siderite, chalcopyrite, manganocalcite, and some decompo- 

 sition products. Specimens of hexagonal calcite, sometimes found 

 here implanted in solitary whiteness on ice-like drusy quartz, 

 are very beautiful. 



The zeolite, in both the specimens found, occurs implanted on 

 a quartz matrix, and in one case the little crystals curved over a 

 crystal of sphalerite. The largest of these harmotome crystals is 

 not quite one centimetre in length. They present principally a 



1 Formation Contemporaine des Zeolithes. The zeolites observed by Daubre were 

 engendered in the matrix rather than deposited. I think it evident that the Glenda- 

 lough zeolite was deposited. Daubre's harmotome or ehristianite, however, is the lime- 

 potash zeolite philipsite of Dana, and is quite distinct from the harmotome described 

 above, which is the barium zeolite. 



