Olivine

“ Augite, however, appears to be more plentiful in the rocks in the form of small roundish grains.
Olivine is of very common occurrence in the Etna [Pg 140] lavas, mostly in round or irregularly shaped grains, but also in crystals which usually exhibit rounded angles.
A specimen of lava from Salto di Pulichello, erupted in 1603, gave well-developed examples of the presence of olivine, and also of plagioclase. The ground mass was found to consist of felspar microliths, and grains of olivine, augite, and magnetite, with some interstitial glass. ”

“ In the cracks of the olivine a dark ferruginous stain is deposited; then on either side of this a layer of fibrous serpentine of pale golden colour (probably chrysotile) is formed; thus the olivine grains seem traversed by an irregular network of associated dark and light strings. The interspaces then seem to be attacked; and they also are converted into serpentine ”

“ An olivine-gabbro from the west side of St. Kilda [7107] is a dark, heavy, medium-grained rock, in which augite and felspar are conspicuous. The microscope shows, in addition, plentiful grains of olivine, with but little original iron-ore, and some apatite-needles. The structure is ophitic, the plates of pale-brown augite enveloping both olivine and felspar. A little brown hornblende and red-brown mica are probably original, the rock showing little sign of alteration. The felspar is labradorite, with albite- and Carlsbad-twinning, and forms elongated rectangular crystals. ”

“ In all the rocks no pyroxene phenocrysts are displayed in the slide; and the olivine phenocrysts, which are very numerous, do not usually exceed 1 mm., though occasionally the average size is 1·3 mm., and not infrequently it is only ·5 mm. In some cases where the larger olivine phenocrysts lie athwart the current of the felspar-lathes, the smaller (·5 mm.) lie with their long axes parallel to the flow. The olivine is either fresh, or it may be beginning to serpentinise in the cracks, or it may be in part hematised. ”

“ The darker layers consist of olivine, and the lighter of plagioclase. This segregation here and there takes the form of rounded masses, where the minerals are more indefinitely gathered together. The affinity of the rock with intrusive sheets is further displayed by the occurrence of abundant - 354 - nut-like aggregates of pale green olivine. Examined under the microscope, flow-structure is admirably seen, the lath-shaped felspars being drawn out parallel to the planes of movement, and giving thereby the peculiarly schistose structure which is so deceptive. ”

“ Olivine.—A silicate of magnesium and iron and a rock-making mineral found only in those igneous rocks which have little or no feldspar. It easily suffers alteration by weathering and passes into serpentine, and in fact is seldom found except when at least partially altered to the fibrous webs of that mineral. The form of the unaltered crystals within the rocks is shown in Fig. 487, 17, and, cut in sections, the mineral appears in more or less elongated hexagons. The hardness of the unaltered mineral is about that of quartz. ”

“ In some cases there are borders around olivine consisting of fibrous hornblende or tremolite and rhombic pyroxene (kelyphitic or ocellar structures) ; spinels and garnet may occur in this zone, and as it is developed most frequently where olivine is in contact with felspar it may be due to a chemical resorption at a late stage in the solidification of the rock. In some gabbros and norites reaction rims of fibrous hornblende are found around both hypersthene and diallage where these are in contact with felspar. ”

“ A little serpentinisation has gone on at the edges and along cracks of a few of the crystals, but, as a rule, the olivine is very fresh; it is never intergrown with felspars. The augite is slightly pleochroic, of a purple to brown tint, in irregular forms, partly in moderate sized crystals and partly in tiny grains in the ground mass. ”

“ Olivine crystallizes in the orthorhombic system, but distinctly developed crystals are comparatively rare, the mineral more often occurring as compact or granular masses or as grains and blebs embedded in the igneous rocks of which it forms a constituent part. ”

“ The specimen free from melilite corresponds342 in structure and composition with the other specimens, except for the absence of melilite and perovskite, and so they may be described together.
All the rocks are porphyritic, since they bear large phenocrysts of olivine. Under the microscope the olivine is colorless and transparent, and only shows indications of serpentinization along the edges and fissures. It contains rounded inclusions of glass, abundant in some sections, besides octahedrons of magnetite, and others that are transparent with a brownish violet color. ”

“ It is also used in pharmacy.
[67] Payen.
OL′IVE. Syn. Olea, Oliva, L. The Olea Europæa (Linn.) , a native of the South of Europe. The unripe fruit is preserved in brine (Spanish olives, French olives) ; the ripe fruit furnishes olive oil; the bark is bitter, astringent, and febrifuge, and has been used as a substitute for cinchona bark; it yields a gum-like substance (OLIVE GUM) , which was formerly reported vulnerary, and contains olivine. The olive tree has in all ages been held in peculiar estimation as the bounteous gift of Heaven to man. ”

“ A stratified rock belonging to the Carboniferous group. See Table L, p. 393.
Olivine. An olive-coloured, semi-trans_parent, simple mineral, very often occurring in the forms of grains and of crystals in basalt and lava.
Oolite, Oolitic. A limestone, forming a characteristic feature of a group of the secondary strata. See Table II. H, p. 391, It is go named, because it is composed of rounded particles, like the roe or eggs of a fish, Etym.,oon, egg, and lithos, stone.
Opalized wood. Wood petrified by siliceous earth, and acquiring a structure similar to the simple mineral called opal. ”

“ The process, as is shown by what we have seen above and what I have described in my paper on the "Lherzolite of the Ariége," apparently consists in the gradual decomposition of the olivine by the action of slowly infiltrated water, during which the hydrous compound serpentine is formed, and the iron thus liberated is thrown down as either Fe2O3 or Fe3 O4, commonly the latter. Mr. Macpherson [20] considers the reaction as a " loss of one fourth part of its (magnesia) base .... ”

“ If magnesia and iron be above the average while silica is low olivine Mineral Constitu-tion.may be expected; where silica is present in greater quantity other ferro-magnesian minerals, such as augite, hornblende, enstatite or biotite, occur rather than olivine. Unless potash is high and silica relatively low leucite will not be present, for leucite does not occur with free quartz. Nepheline, likewise, is usually found in rocks with much soda and comparatively little silica. With high alkalis soda-bearing pyroxenes and amphiboles may be present. ”

“ Lime, abounding phosphates, magnesia, with an abundance of silicates of alum and mercury, and a sufficiency of potash and soda, are the chemical and physical requisites which this tree will find most advantageous to its development, and cause it to produce abundantly, and, provided other circumstances are equal, give the very best oil. It is seen that the olive will flourish wherever its roots will penetrate easily, and there is no deficiency of lime and alkali, such as a loose soil of rocky clay, or sand of volcanic or granite formation. ”

“ Olives are often piled up in a heap and left to rot for six months or a year before being pressed. This suits the national taste; they like strong or rancid oil, but it is not a marketable product and has to be consumed at home.
France has a population of thirty-eight millions, an area of two hundred and four thousand square miles, of which only three hundred and seventy-five thousand acres are given up to the cultivation of the olive. The annual product of oil is only nine million gallons. ”

“ Well, I also, in my life’s experience, have planted olives and watched them grow; and if I were to return to the spot, doubtless by this time I might reap some of the fruit of my labour. Who knows? perhaps the contents of this jar were gathered from those very identical trees! The thought is a pleasant one to myself, and will impart an extra relish to the flavour. That was in a large oil district in Syria, where the whole of the high land was devoted to the cultivation of the olive tree, both for the sake of the fruit and the oil it yields ”

“ The time in which to harvest the olive varies according to climate and the product desired. It may depend absolutely on climate, as the maturity of the olive is hastened and more oil is obtained where the temperature is high and vegetation has the advantage of a vivid light.
So the olive matures earlier and carries more oil at the extreme south of its zone, but the oil is fatty, high-colored and only useful in manufactures or as an illuminant, being utterly useless for food. ”

“ The longer the olive hangs
The more it renders.
This is an illusion. The longer the berries hang on the trees the greater is their exposure to a variety of perils; the birds devour many, more are beaten off by storms, and unless they are taken off the ground immediately, acquire an earthy flavor which renders them unfit for oil making. Another serious danger is that of being touched by frost which diminishes the yield of oil. But even supposing all olives to remain on the tree up to the point of full maturity, they are not making any more oil but are losing water. ”

“ He says, in his lesson on agriculture, "Olive oil is not like the juice of the grape, which requires a chemical process to transform the sugar it contains into alcohol, in order that it may become wine; the oil is there, ready made within the fruit, and the utmost that can be done is to extract it, just as it is, bursting the cells within which it is enclosed, by crushing the olives and then pressing them." "Olive oil is found, not made." ”

“ The fruit is mild, or sharp, or bitter; and the oils differ likewise; so that a pure olive-oil may be unfit for purposes of food, and only fit for greasing machinery and making soap. The green, unripe olives, having had the bitter taste extracted with salt, are preserved in vinegar with spices. The ripe olives are gathered in the fall, when they are as large as common plums. They are of dark-green color, and the pit, now become a hard stone, contains a savory kernel. The flesh is spongy, and its little cells are filled with the mild oil, which runs out at the least pressure. ”

“ The yield of the olive is of two kinds, oil which is well known and amurca, of the use of which many are so ignorant that one can often see it streaming from the mill and wasting upon the ground where it not only discolours the soil, but in places where it collects even makes it sterile: while if applied intelligently it has many uses of the greatest importance to agriculture, as, for instance, by pouring it around the roots of trees, chiefly the olive itself, or wherever it is desired to destroy weeds. ”

“ You see, there's just one little wee speck, essence, or whatever it is, in a gallon of cotton-seed oil, that give it a smell, or a flavor, or something—get that out, and you're all right—perfectly easy then to turn the oil into any kind of oil you want to, and there ain't anybody that can detect the true from the false. Well, we know how to get that one little particle out—and we're the only firm that does. And we turn out an olive-oil that is just simply perfect—undetectable! ”

“ If the berry is left upon the tree the skin finally wrinkles and the color becomes a dull black. This is the state in which it is popularly supposed to give the most oil, which we have already shown to be a fallacy but even granting it to be true, the quality is inferior, the flavor gross and the oil soon becomes rancid. An olive is fully ripe when on being squeezed between the thumb and finger the soft pulp shows no white, but for many reasons, as we have seen, it may be desirable to forestall this period.
No time can be set when an olive crop should be harvested. ”

“ The olive is fond of a chalky soil, that is, one largely made up of lime carbonates. The carbonate of lime is indispensable to vegetable life; and it is noticed, that the oil from olives grown on a calcareous soil, is better than that from a soil lacking in this element. Chalky soils are cold, because they do not easily absorb the heat of the sun. For the same reason red soils are warm, absorbing and retaining a great degree of heat. The best soil for the olive is that in which lime predominates ”

“ One may fail to extract it, one may injure it in the process, it may lose in quality or even become rancid by careless handling or storage, but the one and only object of the oil mill is to extract, clarify and store the oil, while experience and skill will undoubtedly add much to the result of a given olive harvest, the fact remains that the oil is made and in the berry. A mortar and pestle will crush olives and the oil and water can be strained out, through cloth or crash by hand. ”

“ A simple and homely test for the detection of adulteration is the heating of oil until it smokes, in some small vessel. The smell of olive oil while suggestive of the kitchen and cookery is not at all disagreeable, while any counterfeit oil, and especially cotton seed oil, is exceedingly offensive to the nostrils. If placed in a refrigerator, pure olive oil will remain unchanged, or at most throw down a little palmatin, while adulterated oil will thicken and congeal. The persistent adulteration of olive oil will bear its legitimate fruit ”