SCIENCE. 



[Vol. XIII. No. 321 



PLATINUM. 

 The Engineering and Mining Journal calls attention to a re- 

 newed demand during the last year or so for crude platinum, or 

 " platinum sand," and gives a summary of the localities where the 

 metal can be found in this country. There are so many localities 

 in this country where it has been found, that it seems reasonable to 

 believe that a regular platinum-mining industry may at some time 

 be established, perhaps, independently of placer gold-mining. 



The placer mines of California, Oregon, and other States and 

 Territories, have shown a large number of localities in which plati- 

 num occurs. Small lots have come into the market from many of 

 them, and the number would doubtless have been greater had the 

 miners known that the crude metal could be sold in very small 

 quantities. While aware that their " black sand " contained plati- 

 num, it seemed hardly worth while to take the trouble to collect the 

 ounce or so of metal which might be obtained at a clean-up. 



Now that hydraulic mining in California has received such a set- 

 back from invidious legislation, the quantities of platinum found, or 

 to be found, are naturally less than before. Still the known locali- 

 ties, where gold-mining is still carried on by the hydraulic process, 

 or by sluicing from drift or cement mmes, are not few. 



It is very possible that some arrangement of the undercurrents, 

 by which a larger quantity of black sand would be collected with 

 the amalgam, might be profitable. Whenever grizzlies are used, 

 the addition of screens, placed below, might be an improvement. 

 The platinum grains are, as a rule, in better shape for concentra- 

 tion than particles of gold, and they do not flour like amalgam. 



In cleaning up the main line of sluice in placer mines showing 

 platinum, if pains were taken to collect a comparatively large 

 amount of the heavy material, — " black sand," etc., — this, to- 

 gether with the savings from the undercurrents, might be run over 

 some mechanical concentrating apparatus, such as a vanner, with 

 a production of platinum which would pay for the extra trouble. 



But there are possibilities of finding platinum in other than gold- 

 mining regions. Of course, wherever the metals occur together, 

 any method of saving gold by gravity will also result in the saving 

 of platinum, if present ; and when amalgamation is the principal 

 dependence, as in ordinary sluicing, still gravity is mainly relied on, 

 even if plates are also used, to hold or to catch the amalgam, and 

 therefore any platinum which may be present. It may be, how- 

 ever, and very probably too, that there are localities which have 

 been prospected for gold and abandoned as unprofitable, which 

 would furnish platinum hi commercial quantities. The association 

 of the two metals is by no means a necessary condition. That 

 they are in practice found together, simply means that a gravity 

 process which saves the one saves also the other. It is therefore 

 worth while for prospectors exploring new fields to keep an eye 

 open for platinum. 



The same journal is authority for the statement that within the 

 last few days a noteworthy discovery has been made : platinum 

 has been found in place in the nickeliferous ore of Sudbury, Canada, 

 by Professor F. W. Clarke. This discovery was made accidentally, 

 in the course of determinative and analytical work upon the ore, 

 which presents other peculiarities. While the amount found is of 

 little or no commercial importance, it has a very great scientific 

 significance, and is certainly something new. Platinum grains have 

 been found in secondary rocks, such as recent sandstones, con- 

 glomerates, etc. ; but never before, so far as we are aware, in vein 

 stuff, although it has long been looked for, and such an occurrence 

 was to be expected. There is therefore always the chance that ac- 

 tual veins of platinum-bearing material, so often falsely reported, 

 may actually be found, and that perhaps some of them may be of a 

 paying grade. The number of localities, and their wide distribution, 

 in this country, point to such an outcome. 



Granitic quartz, he remarked, is the last mineral to solidify, as 

 may be well seen in such rocks as granite, where it fills the angular 

 spaces between the crystals of felspar and other silicates. 



On the other hand, porphyritic quartz is characterized either by a 

 well-developed crystallographic outline or by rounded or embayed 

 forms derived from such crystals by the corrosive action of the 

 molten lava in which they were suspended. The destructive forms 

 are by far the most common, and their distribution indicates that 

 porphyritic quartz crystallized in the magma at great depths be- 

 neath the earth's surface before the majority of the silicates with 

 which it is associated were formed. Mr. Diller laid special stress 

 on the fact, that, while the silicates are crystallizing in a molten 

 mass, if porphyritic quartz is present it undergoes resorption ; and 

 not until the silicates are developed, and granitic quartz begins to 

 form, does the resorbent action discontinue. 



Mr. Iddings was quoted as having shown that the crystallization 

 of porphyritic quartz is not determined by the chemical composition 

 of the magma, but due to physical conditions ; and the speaker 

 agreed with Lagorio, also, that the resorptive phenomena of por- 

 phyritic quartz and other minerals in eruptive rocks is a conse- 

 quence chiefly of the relief of pressure in the process of eruption. 



To explain the crystallization of silica as porphyritic quartz, 

 right in the face, so to speak, of the iron, magnesia, and other 

 bases which, as we would suppose, were thirsting for the silica to 

 form silicates, Mr. Diller advanced a novel hypothesis as to the in- 

 fluence of pressure on the crystallization of minerals in deep-seated 

 magmas. 



Reasoning from the results of Hallock's observations (Science, 

 xi. p. 152) and other data, he concluded that an increase of the 

 pressure, already enormous, upon the magmas within the earth, 

 only removed them further from crystallization, instead of producing 

 it, as has been suggested by some petrographers. 



At a considerable depth beneath the earth's surface the pressure 

 upon the magma is so enormous, and the difficulty of moving the 

 molecules among themselves so as to segregate those of a certain 

 kind and arrange them in crystals is so great, that the crystallizing 

 force, which has a comparatively small limit of strength, is unable 

 to overcome the resistance, and crystallization is wholly prevented. 

 Thus it would appear that the interior of the earth is maintained 

 in an amorphous condition by pressure alone, and only a compara- 

 tively thin crust allowed to crystallize. It would follow from this 

 view that the crystallization of the magma within the earth is ren- 

 dered possible only by the relief of pressure ; and the minerals 

 which could crystallize first (and they are similar in all lavas) must 

 be determined to a large extent by the relative strength of their 

 crystallizing forces. As a consequence of the gradual relief of 

 pressure, it would be expected that simple minerals such as the 

 oxides, of which quartz is one, could crystallize before the more 

 complex silicates. A further relief of pressure may enable the sili- 

 cates to form, and, in the struggle for silica, the quartz is partially 

 or wholly resorbed. If the rock cools slowly, and becomes holo- 

 crystalline, any silica that is left over after the bases in its neigh- 

 borhood are satisfied will fill put the irregular spaces between the 

 crystals of silicates, and form granitic quartz. 



The production of twinning lamellae in many minerals, of rocks 

 which have been subjected to high pressure, was regarded as a 

 step in the direction of reducing crystallized matter to an amorphous 

 condition. 



The full paper, which is only an abstract of a forthcoming bulle- 

 tin of the United States Geological Survey, will probably be pub- 

 lished in the " Proceedings of the Philosophical Society." 



ETHNOLOGY. 

 The Man of Spy. 



THE HISTORY OF PORPHYRITIC QUARTZ IN ERUP- 

 TIVE ROCKS. 

 In a very suggestive communication with the above title, pre- 

 sented to the Philosophical Society of Washington, Saturday even- 

 ing, March i6, Mr. J. S. Diller emphasized the distinction first 

 clearly drawn by Rosenbusch between granitic and porphyritic 

 quartz in eruptive rocks. 



At a recent meeting of the New York Academy of Sciences, 

 Professor J. S. Newberry described the important finds of human 

 remains in a cave at Spy in Belgium, which were made in 1887, 

 and illustrated his lecture by interesting photographs of the crania 

 and other portions of the find. Since the discovery of the Nean- 

 derthal man, no other discovery of equal importance has been 

 made ; the more so, as Messrs. Ed. van Beneden and Ch. van 



