34 Johnson and Warren — Geology of Rhode Island. 



points conclusively to the presence of chloi'ite so generally 

 looked upon as serpentine heretofore. 



The Vein Minerals. — As noted in Part I, small veins of vary- 

 ing sizes, sometimes attaining a width of an inch, and consisting 

 essentially of actinolite, clinochlore, and hortonolite, are found 

 following the directions of the joints and also cutting irregularly 

 through the rock. Furthermore, these veins are confined in 

 their occurrence to the " chloritic " and " actinolitic " types 

 of the partially altered rock and must be looked upon as one 

 expression of the alteration phenomena of the rhodose. The 

 vein minerals are quite irregular in their arrangement and 

 start immediately from among the grains of olivine and ore in 

 the wall rock. They appear to have formed along joint or 

 fracture lines which afforded easy channels for the mineral- 

 bearing solutions. 



The Actinolite. — The actinolite is the most abundant mineral 

 and its crystals attain a relatively large size, being often from 

 l cm to 2 cm in length. It . is light green to yellowish green in 

 color, prismatic in habit, and is conspicuous by reason of its 

 highly perfect prismatic cleavages. Terminal crystal planes 

 are lacking. Fragments of it under the microscope show a 

 feeble pleochroism from pale to yellowish green and an extinc- 

 tion angle of 15 degrees measured in fragments lying on their 

 cleavage faces. The specific gravity was found with the pycnom- 

 eter to be 3*062 at 20 degrees. A chemical analysis was 

 made of selected crystals of the actinolite which, after crushing 

 to a small grain and handpicking, had been digested in dilute 

 hydrochloric to remove ferruginous matter. The material thus 

 prepared showed no trace of impurity. The analysis and ratios 

 derived from it are given below in column I. It is interesting 

 to note that the ratios bear a close resemblance to those derived 

 by Penfield* from the analysis of actinolite by Stanley, espe- 

 cially to JNo. Ill (p. 32), an actinolite associated with talc 

 from Greiner in Tyrol. For comparison these are given below : 



Si0 2 : E m 2 3 :E II + (F.OH) Si0 2 :E»0 + (F + OH) 



Greiner -938 : -017 : '935 1 -997 



Cumberland -933 : -010 : -916 1 '982 



No determination of fluorine was made in the case of the Cum- 

 berland actinolite but intense ignition in a hard glass tube gave 

 some slight trace of etching, indicating that fluorine is probably 

 present to a slight extent in this actinolite as in all of those 

 studied by Penfield and Stanley. 



The Clinochlore. — The clinochlore is found in the form of 

 psueclo-hexagonal or rhombic tables penetrating the other miner- 

 als and not uncommonly attaining a diameter of from 2 to 5 mm . 

 * This Journal, xxiii, 1907. 



