Analysis of Auriferous Sand. 197 



Magnetite is present in great abundance and in a finely divided state, 

 the largest grains not exceeding a millimeter in length. It forms by 

 weight alone 15 or 20 per cent, of the entire mass, and when the latter is 

 sifted through a sieve of a hundred meshes to the inch it constitutes 44 

 per cent, of this fine material. Crystallographic faces are rare, and though 

 often marred, still oclahedrons (111, 1) of considerable perfection are found. 



Garnet occurs in such profusion that a pink tint is given to a mass of 

 selected grains of uniform size, and its predominance may be considered 

 the chief physical characteristic of the sand. 



Two species were noted : one is a brilliant wine-red variety, which, 

 though not nearly so numerous as its duller relative, occurs more fre- 

 quently in crystals — the trapezohedral faces (211, 2-2) predominating. 

 The other garnet is readily distinguished by its lighter amethystine tint 

 and its greater abundance. OrystallograxDhic faces are somewhat rare and 

 invariably dodecahedral (110, i). In the abseiice of chemical analyses, 

 any statements as to the exact species to which these garnets should be 

 referred would be largely conjectural. Attention is quickly drawn to the 

 perfection of these minute garnets in their crystallographic faces and out- 

 lines, and to their association with rounded fragments of their own kind as 

 well as of other minerals. Have these crystals survived by reason of their 

 hardness or by favoring conditions, or does their preservation suggest the 

 impotency of wave-action in the destruction of minute bodies ? 



Among the black, heavy grains occur individuals which, except in 

 shape and non-magnetic character, resemble magnetite. On crushing be- 

 tween glass slides, thin slivers are obtained which in transmitted light are 

 green, and which, from their cleavage, pleochroism, high index of refrac- 

 tion, small extinction angle, and insolubility in acid, are readily recognized 

 as hornblende. 



Two groups of grains were noted which are distinguishable by slight 

 variation in color. Both are clear-yellowish green, but one is somewhat 

 darker than the other. The optical properties of both indicate pyroxene 

 and possibly olivine. Fortunately a fragment was obtained in the ortho- 

 diagonal zone nearly normal to an optic axis which gave an axial figure 

 of sufficient deflniteness to indicate its optically positive character. A 

 numl^er of grains were selected from minerals of both colors and subjected 

 to prolonged heating in hydrochloric acid without decomposition, indicat- 

 ing that both minerals are pyroxene. 



A few zircons, a fi:-action of a millimeter in size but perfect in form, were 

 found associated with others rounded on their solid angles and edges. 

 The crystals are of the common short form and bear the usual faces in a 

 greater or less degree of development. Pyramids of the first and second 

 order alternate in magnitude ; pinacoid encroaches upon prism, and vice 

 versa. 



Quartz constitutes by far the largest proportion of th© minerals, both in 

 bulk and in weight. It is always fragmental ; sometimes water-clear, but 

 chiefiy occurs in opaque grains of different colors. It is seldom free from 

 material of a higher specific gravity, and is often so tinted as to be almost 

 indistinguishable from magnetite, but readily bleaches in acid. 



27- Nat. Geog. Mag., vol. Ill, iSdl. ■ 



