18 



Staurolite is chiefly admired for often assuming a cruci- 

 form appearance, looking like five crystals, four being 

 united round a fifth. It appears however to be a regularity 

 in the aggregating of the sides, without a sufficiency to fill 

 up the lateral edges — see the lower figure. 



They have been called twin crystals, as if two had passed 

 across each other. 



The whole appearance is somewhat glassy, of a blueish 

 pearly lustre, having a foliated fracture on the broader faces. 

 In other respects it is somewhat conchoidal, and hard enough 

 to scratch glass. 



■ Fusible by the blowpipe into a frothy enamel. It does 

 not form a jelly when combined with acids. But if thrown 

 on charcoal it emits a yellow phosphoric light. 

 On analysis by Klaproth it was found to contain 

 Silex - - 49 

 Baryt - - 18 

 Argil - - 16 

 Water - 15 



98 



Its primitive form is said to be an octaedron, divisible in 

 the direction of the diagonals of the mutual base of the 

 pyramids, so as to form four irregular tetraedrons, or se- 

 parate four solid angles, leaving a rhomboidal dodecaedron, 

 which might perhaps with more propriety have been called 

 the primitive, to save confusion. 



