Vol. 5] 



Eakle. — Lawsonite. 



85 



of the dark green chloritic mass. The identity of these plates 

 with lawsonite was not at first suspected, because of their dis- 

 tinctly different habit and association from the Marin County 

 crystals, and their lack of the characteristic bluish tinge. The 

 plates are basal, seldom more than 2-3 mm. thick, but often a 

 centimeter or more in surface dimensions. Many of them are 

 slightly thicker in the center and taper off towards the edges, 

 giving a characteristic lenticular appearance to the broken edges. 

 These basal planes are the only crystal faces present, the edges 

 being broken and irregular in outline. The plates are appar- 

 ently colorless when pure, but owing to inclusions and impreg- 

 nations of chlorite they have mostly a greenish cast. An analysis 

 sufficient for identification was made of the mineral, but the 

 plates were too much impregnated with chlorite to warrant a 

 complete analysis. 



Analyses. — 1. Analysis by the writer. 



2. Analysis by Ransome and Palache. 



3. Analysis by Hillebrand and Schaller. 



1 2 3 



SiO- 38.43 37.71 38.45 



TiCF 0.36 



AP ° 3 1 33 39 32 43 f 31 " 35 



JW } i6 6V 6 , { 0.86 



FeO 0.10 



MnO trace 



CaO 16.85 18.15 17.52 



MgO 0.17 



K 2 0.23 



Na 2 0.06 



H 2 ignition 9.83 11.31 11.21 



98.50 99.60 100.33 



Macroscopic-ally the rock appears to be a very compact mass 

 of scaly chlorite through which the lawsonite plates are thickly 

 disseminated, but under the microscope, in addition to the chlo- 

 rite and lawsonite, considerable muscovite and also dull brownish 

 irregular grains of titanite or leucoxene are revealed. 



The lawsonite sections are mostly rectangular or lenticular 

 slabs, and their high relief easily distinguishes them from the 



" Amer. Journ. Sci., 1904 (4), 17, 195-197. 



