COMBUSTIBLE MINERALS, NOT GASEOUS. 



181 



CLASS III. 



COMBUSTIBLE MINERALS, NOT GASEOUS. 



This class includes all the combustible minerals, commonly so called, not already noticed, viz ; 



1. Sulphur. 



2. Bitumen. 



3. Amber. 



4. Graphite. 



5. Anthracite. 



6. Coal. 



7. Lignite. 



8. Peat. 



SULPHUR. 



Sulphur. Cleaveland, Phillips and Shepard. — Soufre. Hauy and Beudant. — Native Sulphur. Thomson. — Prismatic 

 Sulphur, or Common Sulphur. Jameson. — Prismatischer Schwefel. Mohs. 



Fig. 14. 



Fig. 15. 



Description. Colour when pure, sulphur-yel- 

 low ; but in consequence of the admixture of foreign 

 matters, it is sometimes red, brown, grey, and even 

 green. Streak white, or sulphur-yellow. It oc- 

 curs regularly crystallized ; also massive, dissemi- 

 nated, stalactitic, and investing other minerals. 

 Primary form an octahedron with a rhombic base. 

 Fig. 14, P on P 106° 38' and 84° 58' ; P on P' 

 144° 17' {Beudant). Sometimes the terminal 

 sohd angles are replaced by tangent planes, as 

 in Fig. 15. Cleavage imperfect and interrupted. 

 Fracture uneven, splintery or conchoidal. Lustre shining and resinous. Varies from trans- 

 parent to translucent on the edges. It possesses double refraction in a high degree. Very 

 brittle. Hardness 1 .5 to 2.5. Specific gravity from 1 .90 to 2. 10 {Phillips). 



When heated and held in the hand, a crackling noise is distinctly heard. It is very fusible, 

 combustible, and even volatile. Burns readily with a blue flame, and is resolved into sul- 

 phurous acid by combination with the oxygen of the air, leaving no residuum when the 

 mineral is pure. It acquires resinous electricity by friction. 



Geological Situation. Sulphur is most common in volcanic countries. It is sometimes 

 found in primary rocks, but is more frequently associated with the secondary and tertiary 

 ones. It sometimes also results from the decomposition of the compounds of which it forms 

 a constituent. 



