OCCURRENCE OF MONOCLINIC AMPHIBOLES. 283 



MONOCLINIC AMPHIBOLES. 



The moiioclinic amphiboles include the following rock-making- minerals: 



TREMOLITE, ACTIXOLITE. CU3OIIXGT0X1TE, GEUAEBITE. EORYBLEXDE, «LAUCOPHA\E. R1EBECKITE, AiVD 



AEFVEDSOXITE. 



Tremolite: 



CaMg 3 Si 4 12 



Monoclinic. 



Sp. gr. 2.9-3.1. 

 Aclinoliie: 



Ca(MgFe) 3 Si 4 12 . 



Monoclinic. 



Sp. gr. 3-3.2. 

 Cumm ingtonite: 



(MgFe)Si0 3 . 



Monoclinic. 

 - Sp. gr. 3.1-3.32. 

 Grunerite: 



FeSi0 3 . 



Monoclinic. 



Sp.gr. 3.713. 

 Hornblende: 



Chiefly Ca(MgFe) 3 Si 4 12 with (MgFe),(AlFe) 4 Si 2 12 , and Na 2 Al 2 Si 4 12 . 



Monoclinic. 



Sp. gr. 3.05-3.47. 

 Glaucophane: 



NaAlSi 2 6 .(FeMg)Si0 3 . 



Monoclinic. 



Sp. gr. 3.103-3.113. 

 Riebeckite: 



jS^FejSiiO^.FeSiO,. 



Monoclinic. 



Sp. gr. 3.3. 

 Arfvedsonite: 



(Na,CaFe) t Si 4 12 -(CaMg) 2 (AlFe) 4 Si 2 12 . 



Monoclinic. 



Sp. gr. 3.44-3.45. 



occurrence. — The monoclinic amphibole group of minerals is one of the 

 most important of the rock-making minerals. Like the pyroxenes, one 

 form or another of amphibole may occur in almost any kind of rock, 

 running from the most basic to the most acid, including both plutonic and 

 volcanic rocks, the unmodified sedimentary rocks, and metamorphosed, 

 igneous, and sedimentary rocks. The amphiboles develop extensively as 

 secondary minerals, and especially is this true for the variety of amphibole 

 known as uralite, which, as seen on pp. 274-275, 276-278, is derived from 

 corresponding pyroxenes. 



Tremolite and actinolite are very abundant in the schists metamor- 

 phosed from carbonate rocks, especially those rich in magnesium and iron. 



