4 



NEW YORK STATE MUSEUM 



PART I 



GENERAL PROPERTIES OF MINERALS 



INTRODUCTORY DEFINITIONS 



The science of mineralogy embraces a knowledge of all natural 

 inorganic substances of definite chemical composition which go 

 to make up the crust of the earth, and, so far as our knowledge 

 extends, of other solid bodies in the universe. 



Minerals, in the sense adopted in the following pages and 

 generally in science, constitute only a part of the mineral king- 

 dom. A mineral must be a homogeneous substance, that is, it 

 must be of the same nature throughout. Many rocks which 

 seem to the unaided eye to be composed of a single substance 

 are shown by more careful examination under the microscope 

 to be made up of more than one substance. A mineral must 

 also have a definite chemical composition as expressed by a 

 chemical formula. Thus, obsidian, or volcanic glass, though 

 frequently quite homogeneous, is not classed as a mineral owing 

 to its lack of definite composition. 



Again, it is customary to exclude from the list of mineral 

 species all substances which have not been formed by the pro- 

 cesses of nature and such mineral substances as have been 

 directly produced by organic life. Under this head are excluded 

 laboratory and furnace products such as the carbonate of 

 lime produced by passing carbon dioxid through limewater. 

 which is not a mineral species though it has the same com- 

 position as the mineral calcite or natural carbonate of lime. 

 Phosphate rock is not classed as a mineral owing to its organic 

 origin though it has essentially the same composition as the 

 mineral apatite which is the natural phosphate of lime. 



The rocks which compose the earth's crust are either single 

 minerals, such as marble, a massive form of calcite, or aggre- 

 gates of two or more minerals. An example of the latter case 

 is granite, composed of three or more separate and distinct 

 minerals which may readily be recognized as different: a glassy 

 mineral showing rough surfaces along the fracture, which is 



