A. F. Rogers— Lawsonite from California. Ill 



should be emphasized, is not an ordinary alteration product but 

 a recrystallized product of metamorphism. 



This lawsonite-cblorite-muscovite rock mass probably repre- 

 sents an original gabbro or diabase. The fact that the chlorite 

 is a diabantite chemically similar to that found in diabase 

 points to the igneous origin. 



A similar rock consisting of lawsonite, chlorite, muscovite, 

 and titanite was collected by Mr. K. JB. Moran at the Fillmore 

 ranch in San Luis Obispo County. The lawsonite occurs in 

 thin plates l mm thick and 6 to 8 mm in diameter. In a thin 



Fig. 8. 



Fig. 



Fig. 8. Lawsonite (J) in quartz (q), Mt. Hamilton region. 

 Fig. 9. Lawsonite in slightly altered diorite, Smith Creek, Santa Clara 

 County (I, lawsonite, h, hornblende, p, plagioclase (andesine), g, glaucophane). 



rock slide the lawsonite appears principally as long rectangu- 

 lar sections with parallel extinction. One elongated section 

 has the peculiar optical properties illustrated by tig. 4. Poly- 

 synthetic twin-lamellse are present in some crystals. 



Eakle 9 also mentions a bowlder of lawsonite- chlorite rock 

 with muscovite and titanite from North Berkeley. 



Smith Creek, Santa Clara County. 



In thin sections of a hornblende diorite collected by Mr. 

 Stephen Taber on Smith Creek, near the Smith Creek Hotel, 

 small crystals of lawsonite were identified. This rock is made 

 up of dark hornblende in a matrix of greenish-gray feldspar. 

 The axial colors of the hornblende are : a — pale greenish- 

 yellow ; /3 = deep green; y = medium green. Absorption 

 /3 > 7 > a. The hornblende is bordered on the ends by a thin 

 fringe of glaucophane in parallel position (fig. 9). The plagio- 



