ROCKS 39 
minerals in the list are essential constituents in some rocks, and accessory 
ingredients in others :— 
I: 
I. Quartz. 5. Biotite. 
2. Felspars. 6. Olivine. 
3. Pyroxenes. 7. Nepheline. 
4. Amphiboles. 8. Leuctte. 
The minerals named in list II. are of less importance—the igneous 
rocks of which they are essential constituents being of more local 
occurrence. As accessory ingredients, however, they play a notable 
part, some of them (muscovite, garnet, schorl, sphene) having a very 
wide range indeed :— ; 
IT. 
1. Muscovite. 4. Garnet. 
2. Sodalite. 5 Seton 
3. Haiiyne and Nosean. _ 6. Sphene. 
The minerals in list III. occur chiefly as accessory ingredients, and 
are thus of subordinate importance to those already mentioned, but they 
are all very widely distributed :— 
III. 
1. Apatite. Beeb yates 
2. Magnetite. 6. Zircon: 
es iimenite. 7:. Rutile. 
4. Hzeematite. 
List IV. includes accessory ingredients which are not so widely dis- 
tributed as those already mentioned :— 
Ve 
Ian opinel: 3. Picotite. 
2. Chromite. 4. Pyrrhotite. 
SECONDARY MINERALS 
There are many minerals of secondary origin, but only the more 
commonly occurring ones are mentioned in the following list :— 
I. Quartz, opal, chalcedony. 7. Muscovite. 
2. Calcite, aragonite. 8. Serpentine. 
3. Zeolites. g. Epidote (Pistazite). 
4. Iron oxides. 1o. Leucoxene. 
5. .Chilorite: 11. Kaolin, etc. 
6. Talc. 
The Law of Mineral Combination—The more important original 
constituents of igneous rocks may be grouped as follows :— 
1. Felspathic Silicates: Felspars and Felspathoids. 
2. Ferromagnesian Silicates: Pyroxene, Amphibole, Biotite, Olivine. 
3. Free Silica: Quartz. 


