482 DOMAIN V. CALCAREOUS. 



MODE IX. GYPSUM. 



Characters. Texture, coarse-grained and loose, commonly 

 with a saline or crystalline appearance. 



Hardness, of course gypsic. Fracture, un- 

 even. Fragments, amorphous, blunt. 



Weight, granitose, sometimes only carbonose. 



Lustre, glimmering. Opake. 



The colour of that of Montmartre is a yellow- 

 ish brown ; but it is also found of various tints 

 of grey : and is sometimes so compact as to 

 resemble coarse limestone. 



As gypsum and alabaster consist of the same 

 peculiar ingredients, though they vary in the 

 mode of combination, it may be proper to begin 

 by considering them on a large scale, and in 

 one point of view. 



In the language of modern chemistry, gypsum 

 and alabaster are sulphates of lime; the sul- 

 phuric acid forming about half of their compo- 

 sition, as the carbonic does in the other cal- 

 careous rocks: hence the gypsous substances 

 do not effervesce with nitrous acid, like the va- 

 rious descriptions of limestone*. 



* Fluor very rarely forms rocks ; but with Phosphorite may be 

 found in the Anomalous division. 



