130 MXVACANE, AND ITS ORES. 



prisms, acntnioated by four planes, which are set on the 

 lateral .planes. 2. In six-sided prisms, which are said some- 

 times to exhibit a tendency to a six-sided acumination. 3. 

 lu acicular and capilliform crystals, v/hose regular shape is 

 no longer determinable, and which are, moreover, strongly 

 compressed. 



The crystals are longitudinally sulcated, often very deeply; 

 are commonly small, and very small, rarely middle sized. 

 The acicular are often fasclcularly aggregated : the capilli- 

 form crystals are often in a singular manner reticulated, the 

 interstices forming equilateral triangles ; exteriorly, shining 

 and moderately glistening ; interiorly, glistening ; the lustre 

 adamantine. 



The principal fracture is foliated with a two-fold cleavage, 

 cutting each other at right angles : the transverse fracture is 

 imperfect and minute conchoidal. The fragments are cu- 

 bical. It sometimes exhibits slendor, columnar, distinct 

 concretions. Is usually translucent, sometimes only trans- 

 lucent at the edges. Hard. Brittle. Gives a pale orange 

 yellow streak. Is easily frangible. Heavy, in an inferior 

 degree, about 4,200. 



on Rutile. 



OBSERVATIONS. 



Observations The larger crystals, particularly those from Hungary, are 

 ofteia curved, have frequent transverse rifts, are sometimes 

 broken entirely across, the ends removed to some distance 

 from one another, and the interstices filled up with the sub- 

 stance of which the matrix consists: sometimes two crystals 

 meet under an angle more or less obtuse, and are joined like 

 the corner of a frame. The crystals are, moreover subject 

 to great irregularities, are seldom fully crystallized, and, 

 therefore, rarely acuminated ; the four-sided prisms are often 

 slightly rhomboidal ; the six-sided prisms, from Hungary, arc 

 usually dilated, and seem composed of accumulated acicular 

 crystals, from whence arise the columnar distinct concre- 

 tions ; the six-sided prisms, from France, are said to origi- 

 pate frctai the truncation of two opposite lateral edges of 

 the four-sided prism ; the capilliform crystals are sometimes 

 coloured green, from chlorite earth. By some authors, 

 this fossil has been said to resemble red silver ore; but the 

 slightest acquaintance with the oryctognostical characters is 

 sufficient to shew the difl'crence ; a geognostical character also 



furnishes 



