Graham — Pseudomorphs in McGill University Collection. 49 



is found in a porphyritic amygdaloid, associated with quartz 

 and chalcedony, conditions under which a feldspar had never 

 been known to occur up till that time; this, and the similarity 

 of the form and habit of the crystals to laumontite subse- 

 quently convinced Jenzsch that the orthoclase was not a pri- 

 mary mineral in the amygdules, but that weissigite is in reality 

 a pseudomorph of orthoclase after laumontite, which was the 

 view held by Blum. 



Similar pseudomorphs are mentioned by Blum as occurring 

 at Niederscheld, near Dillenburg in Nassau. Flesh-red crys- 

 tals of the common laumontite habit are dispersed through 

 the greenstone, associated with quartz, which often completely 

 envelops them ; calcite and prehnite are also present in small 

 quantity. The prism faces of the crystals are striated verti- 

 cally, and the crystals are often more or less split along the 

 directions of cleavage of the original laumontite : the altera- 

 tion to orthoclase is seldom complete. Specimens of the same 

 kind are also found at Schelder Eisenwerk, and at Oberscheld, 

 where crystals an inch in length occur in a druse. 



At Beilstein whole druses of pseudomorphs of orthoclase 

 after laumontite occur in an altered diabase ; the crystals, 

 which are sometimes more than an inch long, have their origi- 

 nal form well preserved, and show the usual strise and cracks 

 along the prism faces; and their pseudomorphous nature is 

 also evident from the hollowness of many of the crystals. 

 There is an almost identical occurrence at Conradsreuth, 

 between Miinchberg and Hof in Fichtelgebirge. 



Laumontite is among the minerals found in the Lake Supe- 

 rior mining region of Michigan, where it occurs in clefts, 

 coated, often completely, by calcite, and sometimes also by 

 . native copper. The laumontite is weathered and shows vari- 

 ous stages of alteration, and has been analyzed by Lewinstein* 

 with the following results ; I refers to a brownish laumontite 

 which readily crumbles, breaking along the cleavage directions, 

 whilst II is of a more weathered material which has become 

 firm and hard, and no longer possesses cleavage. 



I. II. Laumontite. 



Si0 9 



... 57*92 



55*21 



511 



Ai 9 o 3 - — 



Fe.O, ... 



CaO 



MoO .... 

 K 2 



... 10-19 



... ri9 



... 459 .. 



... 1-13 



... 2-58 



22-58 



2-55 



0-98 



1-31 



341 



21-7 



.... 11-9 



Na 9 0._._ 



... 1-14 .. 



3*45 





H 2 0._... 



... 21-26 



1051 



15-3 



100-00 100-00 100-0 



*Zeitschr. f. Chem. u. Pharm., iii Jahrg., 1860, p. 11. 

 Am. Jour. Sci.— Fourth Series, Vol. XXII, No. 127.— July, 1906. 



