CLASSIFICATION OF IGNEOUS ROCKS 



573 



Leucite, K 2 O.Al 2 3 .4Si0 2 

 Nephelite, Na 2 O.Al 2 3 .2Si0 2 - 

 Kaliophilite, K 2 0. A1 3 2 .2Si0 2 

 Sodalite, 3(Na 2 0. A1 2 3 .2Si0 2 ).2NaCl 

 Noselite, 2(Na 2 0. A1 2 3 . 2Si0 2 ).Na 2 S0 4 



ne I 

 kp }-L 

 so I 

 no J 



GROUP ii : 

 Acmite, Na 2 0. Fe 2 3 .4Si0 2 

 Sodium metasilicate, Na 2 O.Si0 2 

 Potassium metasilicate; K 2 O.SiO : 

 Diopside, CaO.(Mg, Fe)0.2Si0 2 

 Wollastonite, CaO.Si0 2 

 Hypersthene, (Mg, Fe)O.Si0 2 

 Olivine, 2(Mg, Fe)O.SiO 2 - 

 Akermanite, 4Ca0.3Si0 2 

 Magnetite, FeO.Fe 2 3 

 Chromite, FeO.Cr 2 3 



FEMIC MINERALS. 



ac"^ 



ns I 

 ks ! 



di 

 wo 

 hy 



ol 

 am 

 mt 

 cm 



^P 



o 



Hematite, Fe 2 3 --------- hm 



HI 



Ym 



Tj 



Ilmenite, FeO.TiO, il 



Titanite, CaO.TiCK . Si0 2 ... - - tn 



Perofskite, CaO.Ti0 2 - - - - - pf | 



Rutile, Ti0 2 ----- - - ruj 



Apatite, 3(3CaO.P 2 5 ). CaF 2 - - - - - ap ^ 



Fluorite, CaF 2 -."■"- - - — - - - f r | 



Calcite, CaO.C0 2 - cc \-A 



Pyrite, FeS 2 - pr | 



Native metals and other metallic oxides and sulphides. J 



Sal, Fern, and Alfer. — For convenience in subsequent discus- 

 sion, we will anticipate the question of nomenclature, and 

 introduce here three terms which will be frequently used. To 

 express concisely the two groups of standard minerals and their 

 chemical characters in part, the words sal and fern have been 

 adopted. The former is employed to designate Group I, 

 mnemonically recalling the siliceous and luminous character of 

 its minerals. Fern indicates Group II, since its minerals are 

 dominantly /hromagnesian. As adjectives to express these 

 ideas the words salic and femic will be used. In certain formulae 

 employed later the words sal and fern will be used in the sense 

 just explained, as indicating any one or all of the minerals of 

 the respective groups. Subsequently other mnemonic syllables 

 will be similarly treated. 



