130 The Monoclinic Pyroxenes of New York State. 



duces a change in position of the optic axes and bisectrices. In 

 a section normal to the acute bisectrix an increase of tempera- 

 ture from 11° to 196° C caused the optic axes of light colored 

 pyroxenes to wander 1° 34' from their original position ; with 

 more intensely colored ones the change was 0° 36'. 



Pleochroism is generally weak, and is found chiefly in the 

 darker varieties, the light colored ones being non-pleochroic. 



The specific heat of pyroxene has been determined on the black 

 diopside from Nordmarken, Sweden, and found to be 0.1830. 



The different varieties of pyroxene may be defined as follows : 



Diopside. CaMgSiaOe or' SiOg, 55.60% ; CaO, 25.90; MgO, 

 18.5. Color white, yellowish, grayish white to pale green, or even 

 black. Crystals often transparent and colorless. The crystals 

 are usually slender and prismatic, and iron is frequently present 

 in small amount. 



Malacolite as originally used referred to a bluish-gray or gray- 

 ish-green variety. Rosenbusch classes under this term those 

 rock-making monoclinic pyroxenes poor in alumina or free from 

 it, and not laminated parallel to the orthopinacoid. Alalite, Tra- 

 versselite and Ganaanite are merely locality names. 



Hedenbergite. CaFeSisOg, or SiOa, 48.40 ; FeO, 29.40 ; CaO, 

 22.20. Occurs in crystals or in lamellar masses, of a black color. 



Sahlite. This is placed by Dana as a sub-variety, but Hintze 

 makes it a full species, having the composition (Mgre)CaSi206- 

 The color is usually grayish green, and the name is derived from 

 the type occurrence at Sala, Sweden. 



Diallage. According to Dana * the composition is near diop- 

 side, but it often contains a considerable percentage of alumina. 

 Its chief characteristic is a lamellar structure due to a parting 

 parallel to the orthopinacoid, sometimes another parallel to the 

 clinopinacoid and less often one parallel to the base. 



Goccolite was first applied to a dark green variety rich in iron 

 from Arendal, but is now used to designate any granular variety 

 of pyroxene. 



AuGiTE includes the aluminous monoclinic pyroxenes. It 

 varies more in composition probably than any of the other var- 

 ieties. Dana gives the composition as CaMgSigOg with (MgFe; 

 (AlFe)2Si06, and Hintze gives it as (MgFe) CaSigOg+CMgFe) 



*System of Mineralogy, 1893. 



