138 



and altogether constitutes most attractive specimens. As a 

 gangue material for mineral lodes it is well known to the 

 miner. Many specimens o£ lode-quartz will be found in the 

 gold and other exhibits. 



The most important physical characteristic is its hardness — T ; 

 it takes the edge off the best steel, and scratches glass with 

 readiness. Its crystalline form is very characteristic, consisting 

 essentially of a six-faced prism capped by a six-faced pyramid. 

 By means of this crystalline form glassy quartz crystals can be 

 distinguished from diamonds with certainty and ease : ilie licilf- 

 'piframid of quarfz is six-faced, that of diamond four-faced. 



Doubly-terminated crj'stal 



of quartz. 



A 



Quartz crystal with the pyramid 



faces unequally developed. 



B 



It generally happens that crystals of quartz grow inwards into 

 a cavity, one end only being developed ; occasionally, however, 

 a crystal grows in a prostrate position, in which case both ends 

 may be fully formed. A remarkably fine doubly-terminated 

 crystal from the Kingsgate bismuth mines near Glen Innes 

 is contained near this case (see Plate YI, and a smaller specimen 

 in case 143). 



Small specimens are exhibited from Pennsylvania, Mount 

 Eemarkable (S.A.), Boorolong, Kingsgate (Glen Innes), 

 Broken Hill (5547, Consols Mine, resting on calcite), and 

 New England. 



Small doubly terminated quartz crystals with a very short, 

 prism, are of frequent occurrence in porphyry. •] 



