6 CRYSTALLOGRAPHY. 

Many more figures might be given for this one species, py- 
rite. The various forms or planes in any such case have, it is 
true, mutually dependent relations—a fact often expressed by 
saying that they have a common fundamental form. But it is 
none the less a remarkable fact, giving profound interest to the 
suvject, that the attraction, while having this degree of unity 
in any species, still, under each, admits of the m jltitudinous 
variations needed to produce so diverse results. 
At the time of crystallization the material is usually in a 
