366 



DESCRIPTIVE MINERALOGY. 



ACHMITE. 



[From the Greek o.y(y.r\, the point of a sword; from the pointed form of the crystals.] 

 Achmite. Phillips, TViomson, Shepard and Beudant. 



Fig. 382. 



Fig. 383. Description. Colour varying from brownish black 



to greenish grey. Streak pale yellowish grey. It oc- 

 curs crystallized. Primary form an oblique rhombic 

 prism. Fig. 382. M on M' 93° 4'. But it usually 

 occurs in the form represented in Fig. 383, the 

 obtuse lateral edges being deeply truncated, forming 

 a six-sided prism terminated by a four-sided pyra- 

 mid. Cleavage perfect parallel with M; less so 

 parallel with the diagonals. Fracture imperfectly 

 conchoidal. Lustre vitreous. Varies from opaque 

 to translucent on the edges. Hardness from 6.0 to 

 6.5. Specific gravity from 3.40 to 3.50. Alone 

 before the blowpipe, it fuses into a black bead, which is attracted by the magnet. It is not 

 attacked by acids. 



This mineral has been referred to pyroxene, some varieties of which it quite closely resem- 

 bles. It differs, however, in chemical composition, the proportion of lime in achmite being 

 very minute. 



Composition. Silica 55 .25, protoxide of iron 31 .25, soda 10.40, protoxide of manganese 

 1.08, lime 0.72 [Berzelius). 



LOCALITIES. 



Achmite was first found in large crystals in feldspar and quartz, at Rundemyr near Kongs- 

 berg in Norway. A mineral closely resembling it in all the characters which I have had an 

 opportunity of determining, is found in long hair-like prisms running through crystals of cal- 

 careous and pearl spar, at Lockport in Niagara county. These crystals are striated longitu- 

 dinally, have a high vitreous, almost metallic, lustre, sometimes tarnished. Colour brownish. 

 Fusible by the blowpipe alone into a black globule, which is attracted by the magnet. It has 

 not been obtained in quantity sufiicient for chemical analysis. 



The above mineral has been called rutile, to which it is not unlike in its external charac- 

 ters ; but rutile is not fusible by the blowpipe. 



