MONOCLINIC PYROXENES. 271 



belt of cementation, although it can not he asserted that the formation of 

 any of these minerals is confined to either belt. 



The paramorphic change of rhombic pyroxene into anthophyllite 

 being one involving lessening of specific gravity and decrease of symmetry, 

 one would expect the change to take place in the upper physical-chemical 

 zone, but I have been unable to ascertain from the literature the facts in 

 this case. 



The formation of actinolite from a rhombic pyroxene requires the 

 assistance of calcite and silica. This reaction is one of sili cation and 

 decarbonation. It occurs with diminution of volume and absorption of 

 heat. As a matter of observation, corresponding with these facts it is 

 well known that the change is a deep-seated one. 



MONOCLINIC PYROXENES. 

 DIOPSIDE, SAHLITE. HEDEXBEBtilTE, Al'GITE, AC3IITE, SPODl'MEXE, WOLLASTOMTE, AND PEl'TOLITE. 



Diopside: 



CaMgSiA- 



Monoclinic. 



Sp. gr. 3.2-3.38. 

 Sahlite: 



Ca(MgFe)Si 2 6 . 



Monoclinic. 



Sp. gr. 3.25-3.4. 

 Hedeabergite: 



CaFeSi 2 6 . 



Monoclinic. 



Sp. gr. 3.5-3.58. 

 Augite: 



Ca(MgFe)Si 2 6 with (MgFe) (AlFe) 2 Si0 6 . 



Monoclinic. 



Sp. gr. 3.3-3.5. 

 Acmite: 



NaFeSiA. 



Monoclinic. 



Sp. gr. 3.50-3.55. 

 Spodumene: 



LiAlSi 2 6 . 



Monoclinic. 



Sp. gr. 3.13-3.20. 

 Wollasionite: 



CaSi0 3 . 



Monoclinic. 



Sp. gr. 2.8-2.9. 

 Pectolite: 



HNaCajSisOg. 



Monoclinic. 



Sp. gr. 2.68-2.78. 



