Haeusler. — Micro6(.o2)ical Stnictioc of Gold. 337 



crystal projects from an irregular crystalline mass. A great 

 number of crystal-faces always cover the more delicate ar- 

 borescent forms of gold and silver. The incrustations of gold 

 on quartz, due to infiltration in ^^-ide fissures, are distinctly 

 crystalline. 



An exceptionally fine specimen of dendi-itic gold, found 

 by Mr. Eeid, of Owharoa, near the Eadical Mine, was covered 

 With large projecting crystals, aiTanged with a certain regu- 

 larity. In most branched specimens the crystals are spread 

 over" the surface without distinct order, though under low 

 power the planes seem to be overlapping each other, especially 

 when they are of nearly uniform size. Even a granular stu-- 

 face suggests crystalline a^gi'egates under low magnifying- 

 power, owing to the brightness of the protruding grains. 

 Also, the apparently-corrugated sm-face of then- lammae, espe- 

 cially those filling narrow fissures in quartz, bear often a 

 strange resemblance to crystalhne structure. 



It goes witliout saying that by breaking up am-iferous 

 (i[uartz in the mortar the gold is very considerably changed, 

 and but for the different angles and striation of the faces,, 

 caused by friction, and u-regular protuberances, many pouaded 

 specimens might easily be taken for irregularly-developed 

 crystals. 



In a few instances the octahedi'al edges are salient, so as 

 to form a distinct ridge. Twins are very rare, and the twin- 

 ning obscm'e. Surface striation is occasionally seen on the 

 larger faces. When the striation is not in accordance with 

 the laws of isometrical crystalhzation it must be accounted 

 for by contact with striated surfaces, quartz, haematite, or other 

 crystals. 



Traces of crystalUzatiou were also observed in the amalgam 

 from ^ tunnel near Owharoa. 



With the true crystals of gold and silver we meet occasion- 

 ally specimens which resemble abnormally - grown crystals 

 very closely, but which are, as measui-ements of the angles show, 

 not isometric. The u-regular gi-owth and ill-defined out- 

 line make careful measurements very difiicult. But few other 

 mineral species were observed in then- proximity, among 

 which irousand is the most common. How these uregulai- 

 forms originated is difficult to explain. Most likely they are 

 j)seudomorphs. Further finds must be awaited before con- 

 clusions can be drawn as to their formation and the composi- 

 tion of the species, the forms of which they take through 

 infiltration in cavities left after the dissolution of the con- 

 tents. 



Some of the arborescent forms are crystallized, the branches 

 being set at an angle of 60' or 120", corresponding with the 

 dodecahedral angle. Others show no sign of crvstalhzation, 

 22 



