Hamilton. — On Platinum Crystals. 403 



ones. These crystals occur in the grains of sand. Their occur- 

 rence is, however, somewhat rare. The common form in which 

 the platinum occurs is round or oval thin plates, or leaves. But 

 the fact that crystals do occur is important, as proving that the 

 iron-sand is their true matrix. Eoughly crystalline platinum also 

 occurs, sometimes with gold crystallised on it, as well as iridium, 

 iron, and native copper. The iron-sand in question is not the 

 ordinary titanic iron-sand of our beaches. It is non-magnetic, or 

 but slightly so, heavier, and lumpier. Lumps of comparatively 

 large size often occur in it, which are iron pyrites derived from 

 wood, and still retaining the original mineral elements of timber, 

 and often some carbon. This is proved from the fact that twigs 

 and small branches are often found along with the sand, com- 

 pletely changed into pyrites, though still retaining the grain, the 

 bark, and all the characteristics of timber. Specimens of these 

 undeniable branches occur where the wood structure is perfect in 

 some parts, while in other parts it is broken up into masses 

 resembling duck-shot, partially fused together. This, I appre- 

 hend, gives us the key to the origin of the sand, which seems to 

 be nothing else but the pyritized debris of ancient vegetation 

 subjected to special conditions, which we may yet come to 

 understand. 



Just as wood is often silicified into stone in large quan- 

 tities, or carbonized into coal, so it would apppear that it 

 may be metallized into the iron-sand of our goldfields, auri- 

 ferous, cupiferous, or platiniferous, from either some obscure 

 conditions of process or inherent quality of the original sub- 

 stance. These pyritized twigs are curiously shrunken to a far 

 smaller size than their original, some of them being reduced to 

 the thinness of needles, whilst still showing wood structure. 

 The iron-sand of many of our goldfields seems to be derived 

 from the breaking down of this pyritized wood by mechanical 

 and chemical means, such as water- wearing and rusting. The 

 sulphur of the pryites is gradually replaced by oxygen to form 

 the magnetic oxide, probably determined by the conditions of 

 deposit, temperature, etc. In this way, the magnetic iron-sand 

 of our beaches would be the ultimate product of timber, after 

 being first reduced to wood pyrites, and then broken down by 

 oxidation and the action of mechanical agents, and finally 

 changed into the magnetic oxide, the other metals crystallizing out. 



This change can actually be effected experimentally by the 

 artificial oxidation of the non-magnetic lumps of wood pyrites, 

 with the production of magnetite in all respects similar to the 

 titaniferous iron-sand of our shores. Either sulphuric or nitric 

 acid will effect this by long continued action. The grains of 

 sand do not dissolve, but become semiplastic, lose their sulphur, 

 and recrystallize into highly magnetic angular grains of the 

 ordinary magnetic iron- sand. 



