IMPORTANT ELEMENTS AND MINERALS 49 
The sulphide of iron, 
pyrites (FeS,), is not used 
as an ore, but is found in 
many of the rocks in the 
form of cubical (or other) 
crystals (Fig. 10), of a 
bronze yellow color, being 
commonly known as 
“fool’s gold.” ‘| 
Gypsum (CaS0,+2H,0). ° 
— This, the sulphate of 
Pre. LL. 
Crystal and massive piece of gypsum. Both 
nearly transparent. 
E 
Fic. 10. 
Cubes of iron pyrite intergrown. 
lime, is produced by 
the decay of many 
lime-bearing minerals, 
or by the alteration of 
the carbonate of lime 
to the sulphate. It is 
soluble in water and 
makes it hard. In 
appearance, gypsum 
bears a certain resem- 
blance to calcite, but 
it is softer, does not 
effervesce with acid, 
and has a_ cleavage 
nearly as perfect as 
