COMPONENTS OF THE EARTH'S CRUST, MINERALS AND ROCKS 125 



Orthoclase and 

 hornblende 



PlaRioclase and 

 hornblende 



Plagioclase and 

 augite 



Plagioclase 



and 

 hypersthene 



"With 

 quartz 



"Without 

 quartz 



"With 

 quartz 



Without 

 quartz 



With 

 olivine 



Without 

 olivine 





Granite 



Quartz 

 porphyry 

 rhyolite 



Syenite 

 Trachyte 



Quartz 

 diorite 



Quartz 

 porphyrite 



Plutonic 

 Diorite 



Volcanic 



Andesite 

 porphyrite 



Olivine 

 diabase 



Basalt 



Diabase 



Augite 

 andesite 



Norite 



Hypersthene 

 andesite 



Sedimentary rocks 



These are, for the most part, deposited in water, and are of 

 three classes, mechanical, chemical and organic. 

 The principal examples of these are: 



r 1 Sand, gravel, sandstone and conglomerate. These 

 are the debris of rocks containing quartz. 



Mechanical { 2 Clay and shale. These are formed of the debris of 



feldspar and the residuum from impure limestone. 



3 Tuffs. Deposits of loose volcanic materials, 



f 4 Kock salt (chloride of sodium), deposited by eva- 



I poration from bodies of salt water. 



Chemical { 5 Gypsum (sulphate of lime), deposited by evapora- 



| tion from bodies of salt water. All sea water 



I contains sulphate of lime. 



[6 Limestone, deposited in oceans from debris of 



J marine animals, corals, mollusks, etc. 



Organic } 7 Q oa \ formed from accumulations of vegetation in 



I 



marshes. 



MetamorpMc rocks 



These have been subjected to heat and pressure usually in the 

 presence of moisture, and have lost their original form and 

 structure. They include the following: 



Gneiss, which ordinarily has the same composition as granite, a 

 with a foliated or schistose structure. ' 



a In modern usage the word gneiss designates only the schistose or foliated 

 structure and any massive rock made schistose by metamorphisrn is called gneiss. 



