108 A. F. Rogers — Lawsonite from California. 



Calaveras Valley, Santa Clara County. 



Lawsonite crystals were found in seams of glaucophane-schist 

 outcrop on the Sunol road in the northern end of Calaveras 

 Yalley. The crystals have the habit of figure 2 with the forms 

 d{0li},<m\ll0\, tfj001j,and b\0l0\. The crystals are grayish- 

 white, measure from 3 mrn to l|- cm in the direction of the &-axis, 

 and greatly resemble some of the Tiburon crystals. The 

 glaucophane-schist itself contains lawsonite, which appears to 

 be more abundant near the seams. 



Loose bowlders of glaucophane-schists from the Arroyo 

 Hondo at the northern end of Calaveras Yalley contain acic- 

 ular crystals in cavities and seams. The crystals, which measure 



only 2 r 



Fig. 4. 



in length, are elongated in the direction of the a-axis. 

 The forms^ present are cjOOl \ , mjllOf, JjOlOf, 

 and <#f 011|, as represented in fig. 3. The optical 

 orientation for most of the crystals is a = a<b = /3, 

 c = 7, but some of the crystals extinguish on the 

 (001) face in two approximate halves as indi- 

 cated by fig. 4. In one part the extinction is 

 parallel and in the other part it is about 5° to 

 the long edge of the crystal. This possibly indi- 

 cates that lawsonite is monoclinic like car- 

 pholite (H 4 MnAJ 2 Si 2 O 10 ), which is chemically 

 analogous to lawsonite. According to Levy and 

 Lacroix* the extinction angle of carpholite is 3° 

 to 5°. 



Fig. 4. Law- 

 sonite from Ca- 

 laveras valley, 

 Santa Clara Co. 



forms c\001\. 



Mt. Hamilton Region, Santa Clara County. 



Minute lawsonite crystals from a narrow 

 seam in a garnetiferous glaucophane-schist 

 (from the Mt. Hamilton region in Santa Clara 

 County (but exact locality unknown) are repre- 

 sented by fig. 5. The habit is tabular with the 

 d\0\l\ % and rajllOf. Optically they resemble 



the acicular crystals from Calaveras Yalley. 



Northeastern Santa Clara County. 



Specimens of glaucophane-schist from the 3250 peak of the 

 Mt. Hamilton topographic sheet of the United States Geolog- 

 ical Survey, which is about ten miles northeast of Mt. Hamil- 

 ton, contain acicular crystals of lawsonite in seams and cavities. 

 The crystals are 3 or 4 mm in length and are imperfect crystals 

 with indistinct faces arranged in parallel position or in subradi- 

 ating groups. There is a fairly good cleavage parallel to the 

 length of the crystals. Fragments are prismatic with parallel 

 *Les Mineraux des Roches, p. 164. 



