492 Transactions. — Geology. 



Art. XLVI. — On Occurrences of Gold in the Coromandel 



District. 



By J. M. Maclaeen, B.Sc. 



[Read before the Auckland Instittite, 20th June, 1898.] 

 Plates XLIX. and L. 



Native gold generally occurs massive or in thin plates or 

 scales. It is sometimes, but rarely, found crystallized as 

 octahedra or rhombic dodecahedra of the isometric system. 

 Still more rarely do cube forms occur. The occurrence to be 

 described possesses all three crystal forms, and was obtained 

 from a " vugh " or cavityin a reef of clear crystalline quartz, 

 adhering very loosely to the quartz crystals, and raised in 

 fanciful shapes above them, resembling, indeed, nothing so 

 much as a butterfly with outspread wings. So marked is the 

 resemblance that even before it had been removed from the 

 reef, and while it was still in situ, the finders had named it 

 " The Golden Butterfly " (see Plate XLIX.). 



The body of the "butterfly" is composed of irregularly 

 shaped isometric crystals, and the " wings," in the main, of 

 five flat lamellar rhombic dodecahedra, so irregularly developed 

 as to present, at first sight, the appearance of flattened mono- 

 clinic prisms. Of these five plates, three are on one side and 

 two on the other, and the three largest present a marked 

 similarity in crystalline form, being formed essentially of a 

 single rhombic dodecahedron divided at one end to form 

 two separate similar crystals (Plate L., figs. 2 and 3). On 

 one side only of the medial line are cube crystals developed, 

 this side being probably the lower when the crystals were 

 in their natural position. All the plates, or "wings," were 

 attached very loosely to the main body by an irregular sub- 

 crystalline projection, as shown in figs. 2 and 3. No gold 

 was found near the specimen. 



Taking one plate .as typical of the rest, and considering 

 one side of it first (fig. 2), it will be found that the basis of 

 the form is a single rhombic dodecahedron divided at one 

 end into two distinct smaller rhombic dodecahedra (i, i). 

 These, as shown by the darker hatching, are surmounted by 

 two more rhombic dodecahedral planes (1, 1), and these again 

 by a succession of at least seven octahedral planes, denoted 

 on the gold crystal bv fine lines. These faces have plane 

 angles of 60°, and interfacial angles of 110° (? 109° 28' 16"), 

 as nearly as I could determine them with the somewhat crude 



