XLIII. A Synopsis of the Common Rocks 



I. THE COMMON ROCK-FORMING MINERALS AND THEIR CHIEF 

 CHEMICAL INGREDIENTS. 



1. Quartz silicon, oxygen. 



2. Orthoclase Feldspar potassium, aluminum, silicon, oxygen. 



3. Plagioclase Feldspar sodium, aluminum, silicon, oxygen, calcium. 



4. Muscovite Mica hydrogen, potassium, aluminum, silicon, oxygen. 



5. Biotite Mica hydrogen, potassium, magnesium, iron, aluminum, 



silicon, oxygen. 



6. Hornblende calcium, magnesium, iron, silicon, oxygen, alu- 



minum. 



7. Augite calcium, magnesium, iron, oxygen, aluminum, silicon. 



8. Calcite calcium, carbon, oxygen. 



9. Dolomite calcium, magnesium, carbon, oxygen. 



10. Salt sodium, chloride. 



11. Gypsum calcium, sulphur, oxygen, hydrogen. 



12. Pyrite iron, sulphur. 



13. Magnetite iron, oxygen. 



14. Hematite iron, oxygen. 



15. Limonite iron, oxygen, hydrogen. 



16. Siderite iron, carbon, oxygen. 



17. Kaolin hydrogen, aluminum, silicon, oxygen. 



2. THE SEDIMENTARY ROCKS. 



a. Fragmental Rocks: 



Gravel beds made of pebbles derived from other rocks. 



Conglomerates consolidated masses of pebbles. 



Sand beds finer fragments, usually quartz grains. 



Sandstones consolidated sand beds. 



Clay beds disintegrated feldspar, hornblende, etc. 



Shale consolidated clay beds, splitting readily. 



b. Chemically-formed Rocks: 



Stalactites, etc. carbonate of lime, deposited in water. 

 Iron deposits some iron ores, ex. bog iron. 

 Silicious sinter silica deposited in water. 

 Salt sodium chloride. 

 Gypsum sulphate of lime. 



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