Syenite

“ Fig. 16.—Syenite-porphyry, Gebel Zergat Naam [11,512] , as seen between crossed nicols, × 10. f, porphyritic felspar (orthoclase) ; h, hornblende; g, microgranitic ground mass containing felspar, hornblende, and some quartz.
The syenite of Gebel Zergat Naam [11,515] rises as a great boss from among the surrounding dark schistose rocks. It is typically a pinkish-brown rock of rather fine grain (see Plate XXIII) , in which can be seen shining crystals, three to four millimetres long, of [284] pink orthoclase, and specks of dark hornblende, with here and there a little glassy-looking quartz. ”

“ Hornblende, which we have observed to be an important and rather constant constituent of diorite and syenite, is much less abundant in norite; but its place is taken by augite and the allied minerals, hypersthene and enstatite. Black mica is common in norite; but white mica, orthoclase, and quartz rarely occur.
Norite is the most basic of all the feldspathic rocks, as gneiss is the most acidic; while syenite and diorite stand as connecting links, forming a gradual passage between the two extremes. ”

“ I hold it necessary however that the word syenite, if it is to be used as a generic term, should be limited, as rigidly as the ever varying and mingling composition of rocks will admit, to those compound rocks which are akin to greenstone in their chemical and essential characters, or consist of certain notable and distinct proportions of felspar and hornblende, but in which the felspar is either the predominating ingredient, or is crystallized in masses so large and distinct as to remove the compound from those similar compositions now generally known by the name of greenstone. ”

“ The limestone, which at a greater distance from the granite contains shells, exhibits no traces of them near its junction, where it has been converted into a pure crystalline marble. [4] MacCulloch pointed out that the syenite here, as in Raasay, was newer than the secondary rocks, and Mr. Geikie has since shown that there is a strong probability that this Plutonic rock may be of Miocene age, because a similar Syenite having a true granitic character in its crystallisation has modified the Tertiary volcanic rocks of Ben More, in Mull, some of which have undergone considerable metamorphism. ”

“ That a polished surface of granite should weather more rapidly than a rough one is perhaps hardly what might have been expected. The same observer remarks that, though the polished surface of syenite was still bright at the end of not more than three years, it was less so than at first, and in particular that some figures indicating the date, which he had written on it with a diamond, had become entirely effaced. ”

“ The light coloured rocks which belong so the group appear in all cases to consist of the several varieties of syenite which will be described hereafter, while the dark ones, with the exception of some greenstone, seem to be every where formed of clinkstone. The tendency of these syenitic substances to decomposition, explains the weathered appearance of the mountains which I have characterized by the name of the Red Hills, and the accumulation of the fragments which result from it, accounts for the roundness and tamemess of their outline. ”

“ These rocks, like common granite and gneiss, frequently contain epidote as a constituent incidental part, and in this also they are distinguished as well from that syenite to which I propose to limit the term, as from the greenstone of the trap family, since epidote is but very rarely found among these latter rocks. They are equally distinguished from them by the frequent presence of another mineral which, as well as the former, is peculiar to the elder rocks, Sphene. ”

“ It is difficult to assign an origin to this rock, but a variation of it [11,532 B] has been already described (p. 339) as probably an altered syenite, and the main rock may therefore represent the extreme form of alteration of an igneous rock rich in lime felspars. ”

“ In consequence of their more basic composition, diabase and diorite are usually strongly contrasted with granite and syenite in color and specific gravity, being darker and heavier. The basic rocks, too, decay much more readily than the acidic. ”

“ The presence of quartz would make this rock into a granite. Such a compound rock has its type form, and when the proportions of the component minerals are changed, it grades into other types.
Like the granite, syenite is an intrusive rock, which occurs in stocks and batholiths along the axes of present or past mountain ranges. The original magma welled up under the mountain folds, where it cooled slowly, metamorphosing the adjacent rocks. Like granite it has only been exposed after a long period of erosion has removed the overlying layers of rock. ”

“ The most frequent, and apparently the latest type, shews very large blocks of a dark grey rock, a syenite or trachyte, cut to a uniform rectangular oblong form, the outer faces, which are nearly smooth and slightly convex, being cut in towards the joinings of the other stones. ”

“ In places they contain feldspar and pass into syenites; in others the rock is almost pure hornblende. The greater portion of these rocks are of metamorphic origin. The dip is generally vertical, strike east and west to northwest. The syenites are followed by mica schists, and these by coarse biotite granite about 5 miles above Howe Station. In the granite are many pegmatitic veins, carrying biotite, garnets, and tourmaline. Fine-grained granite, varying at times to syenite, forms the rock along the cañon for many miles below this point. ”

“ This rock is unfossiliferous. The disintegration of the syenite from the usual atmospheric agencies is rapid enough; but the resulting detritus does not contribute to form a good clay.
If an artificial section be made of the soilcap, or if advantage be taken of a landslip to examine it carefully, it will be seen to be composed of a dense network of interlacing roots, containing in its interstices a small quantity of black mould, the latter increasing in proportion as the basement rock is reached. ”

“ They do not contain quartz, as that mineral and nepheline are mutually exclusive. From ordinary syenites they are distinguished not only by the presence of nepheline but also by the occurrence of many other minerals rich in alkalis or in rare earths. Orthoclase and albite are the principal felspars; usually they are intergrown to form perthite. In some rocks the potash felspar, in others the soda felspar predominates. Soda-lime felspars such as oligoclase and andesine are rare or entirely absent. Fresh clear microcline is very characteristic of some types of nepheline-syenite. ”

“ The sienite is unstratified, cropping out in independent masses, but rent into pieces mostly of a rhombic figure, the natural joints of which are generally rusty.
It is finely granular, composed of felspar of a blood red, flesh red, or greyish colour, with some quartz, hornblende, and black mica, besides two ingredients, accidental but not uncommon, namely, iron pyrites and small garnets. ”

“ Sienite is the prevailing rock on the east side of Connecticut river in the primitive region, more particularly in the southern part. In some places a narrow stratum of mica slate lies next to the conglomerate of the secondary formation, and a low range of graphic and common granite has been observed in Amherst and Leverett, lying next to the mica slate. Other veins of granite also traverse the sienite; and gneiss occurs in many places. The proportion of hornblende in the sienite is generally small, and mica is often present in considerable proportion. ”

“ Though Syene, by its situation should be healthy, the general complaint is a weakness and soreness in the eyes; and this not a temporary one only, but generally ending in blindness of one, or both eyes; you scarce ever see a person in the street that sees with both eyes. They say it is owing to the hot wind from the desert; and this I apprehend to be true, by the violent soreness and inflammation we were troubled with in our return home, through the great Desert, to Syene.
We had now finished every thing we had to do at Syene, and prepared to descend the Nile. ”

“ The slate near Harwington meeting-house contains a great quantity of sulphuret of iron. Mica slate likewise lies on the sides of the gneiss range in Canaan and Salisbury, where it dips under the limestone. Sienite is scattered on the surface in large masses, especially where the porphyritic gneiss is found. Sometimes, however, the masses are so large as to form mountains. Mount Tom, between Litchfield and Washington, is of this nature, being entirely composed of sienite, resting on gneiss. ”

“ Sniatynski unconsciously replies to this question in these words: "I have heard or read that gold nuggets have sometimes a large admixture of quartz, which must be crushed in order to get at the gold. I suppose your heart is thus covered with an incrustation, that only partly melted while you were staying at Ploszow. You did not remain long enough, and simply had no time to let your love grow sufficiently strong. You have, maybe, energy enough to act, but not enough to decide; but you would have found the energy if the feeling had been powerful enough. ”

“ The cyanide liked the gold better than the potassium, but it has the bad taste to prefer zinc even to gold. It releases the gold and flies to the embrace of the zinc. The gold, suddenly deserted of the friendship of the cyanide, powders down to the bottom of the tank, in absolutely pure form, ready to be melted down into bars. By other processes, which I won't bother you by describing now, the zinc is released from the cyanide, and the cyanide is led to its old friend the potassium, ready to begin work anew. ”

“ Still another good system is the rare feldspar, sanidine, which is excellent for both potassium-argon and rubidium-strontium age determination. Sanidine usually is found in volcanic ash falls and has been important in the establishment of the geologic time scale, as we shall see.
Whole Rocks
Finally there is still another way of obtaining a closed system by using the whole rock, not just a crystal of a single mineral within it. A large body of granite or similar rock may contain a number of minerals, some or none of which may be closed systems. ”

“ Of course, I know that an odour of peach-blossom in the air, resulting in death, could only be associated with some vaporous effluvium of cyanogen, or of hydrocyanic ('prussic') acid, or of both; and when I at last managed to examine some of the dust under the microscope, I was not therefore surprised to find, among the general mass of purplish ash, a number of bright-yellow particles, which could only be minute crystals of potassic ferrocyanide. What potassic ferrocyanide was doing on board the Boreal I did not know, and I had neither the means, nor the force of mind, alas! ”

“ Cyanide, you see, is about the swiftest and painfullest thing out. Before I could move to do anything, I knew he was dead—poisoned and drowned and dead. The coil of wire that had tripped him had gone into the vat with him. ”

“ Cyanite is colorless to bluish-white, sky-blue, berlin blue, yellowish- and reddish-white, gray, and green.
The hardness is 5 to 7, specific gravity 3.45 to 3.70, lustre vitreous and pearly; it is infusible before the blow-pipe, but fuses with borax; is not attacked by acids, and is composed of:
Cyanite is found in Switzerland, the Tyrol, Styria, Carinthia, Bohemia, Norway, Finland, France, South America, Scotland, Ireland, Siberia, the East Indies, and the United States. ”

“ You may think it is pleasant to go through the jungle at night. Brr! I would not go a second time for anything, unless I again needed quinine."
Saying this, he left the astonished little maid while he went to the "men's quarters," selected from a supply of figs the smallest one, hollowed it out, and filled the center with quinine, taking care that the dose should not be greater than those powders which he had received in Khartûm. After which he left the tree, poured tea into a utensil with water, and returned to Nell with the remedy. ”

“ Almost any organic substance can be used as a reducing agent, but it is well not to select one which melts, swells up, or gives off much water and gas when heated in the furnace.
Potassic Cyanide is an easily fusible and somewhat volatile salt, which, when fused, readily removes oxygen and sulphur from metallic compounds, and forms potassic cyanate or sulphocyanate as the case may be. Commercial samples vary much in purity; some contain less than 50 per cent. of the salt. For assaying, only the better qualities should be used.
Iron is a de-sulphurising rather than a de-oxidising agent. ”

“ But she breathed so regularly and calmly that Stas ceased to regret the last quinine powder. He felt that danger of fever was removed and commenced to reason thus:
"The ravine continually leads upwards and even now is quite steep. We are higher and the country is drier and drier. ”

“ Cyanuric acid, deprived of its water of crystallisation, is distilled in a retort, and the product collected in a well-cooled receiver.
2. (Liebig.) A current of sulphuretted hydrogen gas is passed through water in which cyanate of silver is diffused, the process being suspended before all the cyanate of silver is decomposed.
Prop., &c. Cyanic acid is a limpid, colourless liquid; it reddens litmus; is sour to the taste; possesses a modified sulphurous odour, similar to that which is always perceived when any of its salts are decomposed by an acid; it forms salt with the bases called CYANATES ”

“ The zinc becomes oxidized by the separation of oxygen from the fluid on the surface with which it is in contact, whilst hydrogen gas is liberated at that surface touched by the other metal. Here we have, in the first place, a chemical change effected, then a peculiar muscular disturbance. Each successive combination or decomposition, like a pulsation, is transmitted along the circuit from one extremity to the other. How the impulse which is derived from the zinc is transmitted through the body of the animal, or the tongue, to the silver or copper is the next consideration. ”