Schaller and Hillebrand — Chemical Notes on Lawsonite. 195 



Art. XY. — Crystallographical and Chemical Notes on 

 Lawsonite ; by W. T. Schaller and W. F. Hillebrand. 



Crystals of lawsonite are very simple in their combinations, 

 the common forms being the prism, base and brachydome. 

 Two habits occur; tabular crystals with jOOl} and jllOj and 

 crystals with the forms |H0J and jOHJ. The brachypinacoid 

 and the brachydome j Oil \ also occur. A large number of 

 crystals from the typical locality in Marin County, California, 

 were collected by the writer and carefully examined with a 

 hand lens for any additional forms. Only two new forms 

 were determined. 



The forms observed on the six crystals measured are : 



c = = 001 d = 01 = Oil 



5 = 0oo=010 6 = 04 = 041 



m— oo =110 r— "I—I'll 



s= 3. = 331 



The angles measured, with those calculated for these forms, 

 are quoted in the table following : 



Symbol. Measured. Calculated. 



Jo. 



Letter. 



Gdt. 



Miller. 



^ 



P 







— \ 

 P 



1 



C 







001 







0° 02' 







0° 00' 



2 



b 



Ooo 



010 



0° 00' 



90 00 



0° 00' 



90 00 



3 



m 



00 



110 



56 22 



u 



56 22 



a 



4 



d 



01 



011 



09 



36 36 



00 



36 27 



5 



e 



04 



041 



00 



71 18 



a 



71 18 



6 r 2 221 56 27 69 10 56 22 69 27 



7 s 3 331 56 22 76 21 " 75 58 



The new pyramid r = 2 = .{ '221 \ is present on two crystals, 

 the^ faces giving good reflections. Fig. 1 shows one crystal on 

 which this form occurs. 



The new pyramid s = 3 = \331\ is present on only one 

 crystal and but one face of the form occurs. The relative size 

 of the face is about the same as that of the preceding pyramid. 

 The reflection was fair. 



_ The brachy domes are usually deeply striated, rendering it 

 difficult to determine with certainty any domes present. On 

 two crystals, reflections were obtained from two faces, measure- 

 ments of which agree with the angles calculated for the form 

 \ 034 } . The form is rather uncertain and is not included with 

 the others. 



