tark] some COMMOX MINERALS 315 



board for partitions. If manual training is taught the making of 

 a box to hold twenty-five or fifty minerals would be a very good 

 and useful exercise. A large class-room collection could easily 

 be built up also. The specimens should be properly labeled and 

 the finder's name given. Such collections are useful and orna- 

 mental when properly arranged and are no trouble to maintain 

 or preserve. If the school is located in a region where mining 

 is carried on the work and its value will be doubly interesting. 

 In other regions the collection will be found useful in the work 

 in geography in discussing various industries, especially mining, 

 quarrying, and manufacturing. But the priman,- value lies in 

 the actual working knowledge the child will acquire of the com- 

 moner rocks and minerals and of the uses of the same. And this 

 knowledge can be imparted to the child through the medium 

 of its own interest and desires. We do not have to wait until the 

 children are in high school to give them their first introduction 

 into the inorganic world. 



It is the object of these papers to give to the teacher the 

 characteristics and simpler methods of determining the commoner 

 minerals and rocks, so that those teachers who are not versed in 

 the subject may be enabled to include inorganic material in their 

 nature study work. 



A mineral may be described as a substance, found free in na- 

 ture, having a definite chemical composition, and a certain definite 

 shape, and as being inorganic in origin. Some parts of this 

 definition need modifying and explaining. For instance the 

 chemical composition is not absolutely exact in all cases. Some 

 minerals have approximately a definite composition but we cannot 

 say it is exact as for instance it is in quartz, which is silicon and 

 oxygen in the ratio of one of the first and two of the last, or us- 

 ing chemical symbols for these elements. SiO;;. Further a pearl 

 is not a mineral because its formation is due to an organic process, 

 taking place in the oyster. It is well known that all substances 

 are composed of molecules. The shape of the mineral, or its 

 crystal form, is due to the definite arrangement of these molecules. 

 While we cannot enter into this subject here, we can say that 

 mineralogists have found that all minerals arrange their molecules 

 about six diflferent systems and all the crystal forms found in 

 nature can be reduced to these six systems. These systems have 

 names which suggest in a general way the shape of the crystal 

 belonging to them. Thus, isometric (equal+measure) in which 

 the crystals are the same size in all directions. The mineral, 

 galena, is an example of this and occurs in cubes (see fig. 3). 



