Quartz

“ In the middle of the mountain, between the granite rocks, I found broad strata of brittle black slate, mixed with layers of quartz and feldspath, and with micaceous schistus. The quartz includes thin strata of mica of the most brilliant white colour, which is quite dazzling in the sun, and forms a striking contrast with the blackened surface of the slate and red granite. ”

“ Quartz ledges and bands, which are the grateful solutions of many of our cliff problems, are treacherous. Quartz brittles off, in crystals or in masses, in unexpected directions. We cannot test it adequately until our full weight comes upon it; when it may be too late. And so we never step on to projecting quartz, or scale the vertical face of a seam, unless we have hand or foot hold upon good rock above or below it. Happily, quartz seams are usually narrow. ”

“ I have already described a quartz rock as passing by a regular transition to granite, and here the granite in the vicinity of the quartz rock is found to have a foliated tendency, a tendency which not improbably unites it at some point with the quartz rock, although I did not discover that point of perfect transition. ”

“ Some by their refulgent splendor rival the colors of the painters, others the flame of burning sulphur or of fire quickened by oil.”213 Possibly some brilliant varieties of iridescent quartz—“iris” quartz, possessing an internal fracture, displays with great brilliancy all the colors of the rainbow, sparkling with wonderful clearness in its field of transparent mineral—might excite the admiration of one who had never seen an opal. Referring again to these quartz crystals, they are often cut so as to form a dome of quartz and are even used as distinct jewels. ”

“ The three principal agencies that have taken part in the formation of quartz are heat, water, and organic life. When we examine, by the aid of the microscope, certain forms of quartz, such, for instance, as the crystals occurring in some of the quartz porphyries, and occasionally in the pitchstones, as well as much of the quartz of granite rocks, we find that they contain minute cavities which inclose very frequently tiny crystals of other minerals ”

“ Highly crystalline quartz veins render the rock surfaces even rougher than they would otherwise be, and in a few places the face of the rock is covered with egg-like projections, each containing a core of quartz. ”

“ The glazed or polished surface of the quartz rocks at the Pipe Stone Quarry, I consider a very interesting subject, and one which will excite hereafter a variety of theories, as to the manner in which it has been produced, and the causes which have led to such singular results. The quartz is of a close grain, and exceedingly hard, eliciting the most brilliant spark from steel; and in most places, where exposed to the sun and the air, has a high polish on its surface, entirely beyond any results which could have been produced by diluvial action, being perfectly glazed as if by ignition. ”

“ Grey quartzy rock, with a basis of a compact splintery appearance, containing imbedded grains of transparent quartz.Small grained breccia, of which the basis is an earthy-looking mixture of felspar and quartz, resembling clay stone, or compact felspar, and uniting angular and rounded fragments of quartz.An uniform aggregate of large grains of felspar and of transparent quartz, without the aspect of granite, since all the grains appear to have been mechanically rounded and re-united. ”

“ Ascending towards the summit, the quartz gradually increases in quantity, till at last it becomes the prevailing ingredient of the rock, and preserves it against the natural causes of decay; whilst lower down, where the felspar abounds, the rock is extensively disintegrated. ”

“ When studied in thin section, the massive beds of quartzite show more decided effects of dynamic action than at Devil’s Lake. However, the major portions of the grains of quartz have distinct cores which are often beautifully enlarged. ”

“ Quartz.—The most abundant of all minerals, existing as a constituent of many rocks, composing of itself the rock known as quartzite or quartz rock and some of the sandstones and pure sand, forming the chief portion of most mineral veins. ”

“ PHYSICAL PROPERTIES OF QUARTZ, CRISTOBALITE AND TRIDYMITE.
In nature, quartz is the crystalline form most commonly encountered and is so abundant that the term quartz is often used in place of the general term crystalline silica [6, 7] . Quartz is abundant in most rocks and soils and is also present in sand, mortar, concrete, fluxes, abrasives, construction aggregate, porcelain, paints and brick [8] . ”

“ The last bed of quartz rock in this direction is immediately followed by a bed of limestone, and this again is succeeded by an alternation of beds of schist, limestone, and quartz rock for some hundred yards below that bridge, together with masses of porphyry both of a reddish and a greyish colour, but whether disposed in beds or veins I have been unable to ascertain, though I imagine that they are beds, since they seem to conform to the stratified rocks. As this collective mass presents some interesting circumstances it will require a more minute detail. ”

“ The most crystallized and pure specimens of quartz rock afford this variety, and examples of it are to be found every where among the more compact beds of that rock. We may therefore conclude that the avanturine, so much esteemed and long so ill understood, is a variety of quartz rock ”

“ When molten masses of igneous rock were cooling the quartz crystals had their faces interfered with as they grew, and we have resulting crystalline quartz, simply filling in the spaces between the other crystals, such as feldspar and mica, in the granite. Quartz is a large component in many igneous rocks, also in metamorphic rocks, and certain sedimentary rocks like sandstone are almost wholly made up of quartz grains. Quartz is also the gangue mineral in many veins. ”

“ A third mineral, harder than steel, breaking along irregular surfaces like broken glass, we identify as quartz.
How granite alters under the action of the weather may be seen in outcrops where it forms the bed rock, or country rock, underlying the loose formations of the surface, and in many parts of the northern states where granite bowlders and pebbles more or less decayed may be found in a surface sheet of stony clay called the drift. Of the different minerals composing granite, quartz alone remains unaltered. Mica weathers to detached flakes which have lost their elasticity. ”

“ As we approach the summit of the mountain, the quartz rock becomes established to the exclusion of the schist, and it continues to the top, where it offers that aspect of complete disintegration before described under the heads of Jura and Assynt, which covers the tops of the quartz mountains with ruins, and gives them that acute apex and regularly conoidal declivity, which, as far as I have yet observed in Scotland, is sufficient even at a distance to indicate the nature of the rock of which they are composed. ”

“ In Glen Tilt I have taken out specimens from the beds exactly similar to those long compressed and smooth cylindrical bodies which are sometimes found in secondary sandstones. This shows another distinct point of agreement between quartz rock and those sandstones. In the same place is found a very interesting variety. It consists of a regular and repeated alternation of quartz with common argillaceous schist; the smoothest variety of clay slate. The quartz at the same time is compact and crystalline, differing in no respect from the most common specimens of this substance. ”

“ It is abundant as a colorless, transparent substance; it also appears as a brilliant crystal. The name quartz is from the German zwerg, meaning dwarf. Similarly cobalt and nickel are from German words for sprites, the gnomes being little creatures that work the mine of the gods.
In its crystalline form quartz includes amethyst, cairngorm, citrine, quartz cat’s-eye, rock crystal, and rose quartz. Another main group in the quartz family is chalcedony, which includes agate, bloodstone, carnelian, jasper, moss agate, onyx, sard, and sardonyx. ”

“ Quartz is exceedingly abundant in all the great groups of rocks. It constitutes the main bulk of sandstones, is common in shales, and occurs in certain other strata. In many igneous rocks, like granite, it is a very prominent constituent. ”

“ Quartz is found among these rocks in the usual variety which it exhibits when it is an inmate of trap. In its simplest form it is a crust investing a cavity, and terminating interiorly in assemblages of crystals of various sizes and of various colours, white, brown, and amethystine. The exterior quartzy crust often puts on the character of chert, sometimes that of chalcedony; not infrequently the chalcedony appears in the form of a stalactite, of which the several icicles are encrusted with beautiful and crowded assemblages of crystals. ”

“ Many of the specimens found were transported stones, but in many other instances, which I have had occasion to notice in a paper on Glen Tilt, [1] the transition from quartz rock to granite is to be seen in situ. I have there also noticed that, which ought for the sake of uniformity to be repeated here, that the beds of quartz rock which are in immediate contact with the granite often pass into it by insensible degrees. It is well known that there is a gradual transition from mica slate into gneiss, and that this rock again by degrees equally evanescent passes into granite. ”

“ The porphyry is of a red-brown colour, consisting of grey paste with crystal of felspar and angular fragments of slate and granite sometimes one foot in length. The granite contains little mica, and the quartz frequently is arranged in rhomboidal crystals nearly parallel to each other; it readily decomposes, and from the predominance of quartz forms a coarse gritty soil. Quartz-rock forms large beds and veins in the granite, and has a general trend north and south. ”

“ This very irregular mass of rock consists of granite and quartz rock united. The quartz rock is of a peculiar aspect, being of a bluish colour, very uniform and compact and approaching near to common quartz in character, but still shewing evident marks of foliation. It is disturbed and intersected by the granite in a way which I need, not now repeat. A thin stripe of limestone and schist may also be seen interwoven in the granite. Below the cascade there is once more a blank alluvial space of 100 yards, which is succeeded by quartz rock for about the same space ”

“ Sometimes the mineral is imbedded in limestone, in the form of nodules, thus indicating their original connexion with it.
[225]
The varieties, so far as I have observed, are quartz, hornstone, flint, jasper, and semi-opal; and several, which to me are non-descripts. Quartz is the most abundant. It is found of different colours; compact, and porous or cellular; of every size; simple and associated with other silicious stones; massive and crystallized. In Augusta and Rockbridge counties in Virginia, beautiful crystals of quartz, of a singular form, are found. ”

“ Pure white quartz, formed of semitransparent amorphous grains, but the mass has a fracture intermediate between the granular and splintery. From Sky, and alternating with micaceous schist. A similar rock from Balahulish, of a pink colour, but with an aspect more harsh and dry, resembling common secondary sandstone. In the same situation. Pure granular quartz in the same situation, but the grains of large size, and the fracture consequently very coarse. ”

“ While the nature of these strata, which present alternations of red sandstone with graywacké schist, and with indurated grey and blue granular quartz, would incline us to rank them among the secondary rocks, some doubt is thrown on that conclusion in consequence of the peculiar relation they bear to the older rocks which they follow, the gneiss, and the micaceous and chlorite schists. ”

“ This quartz rock is stratified, although vertical, in beds which, as far as they can be seen, appear absolutely and nicely parallel, their lines of separation being defined with a most mechanical exactness. They have a tendency to break into rhombic and prismatic fragments, by fissures perpendicular to their stratification, and being thus broken, they have fallen on all sides around the summit, producing the same appearances as those exhibited by the Paps of Jura, and the mountains of Assynt ”

“ QUARTZITE, in petrology, a sandstone which by the deposit of crystalline quartz between its grains has been compacted into a solid quartz rock. As distinguished from sandstones, quartzites are free from pores and have a smooth fracture, since when struck with the hammer they break through the sand grains, while in sandstones the fracture passes through the cementing material and the rounded faces of the grains are exposed, giving the broken surface a rough or granular appearance. The conversion of sandstone into quartzite is sometimes the work of percolating water under ordinary conditions. ”

“ A thin plate of quartz, such as is often found in the slices of rock sections employed for microscopic investigation, of muscovite granite or quartz porphyry for instance, and which is usually about one-fiftieth of a millimetre in thickness, shows brilliant colours in a parallel beam of polarised light, the Nicol prisms of the polarising microscope being crossed for the production of the dark field before the introduction of the section-plate on the stage. ”

“ This cement may cause effervescence, being often formed of chemically deposited calcium carbonate.
When we consider the distribution of quartz in nature, we look to igneous and metamorphic rocks for the origin of the grains in sandstone. Quartz is one of the commonest minerals; but in granite and quartz-diorite it rarely forms more than half the bulk of the rock, felspar and mica and hornblende being its associates. Veins of quartz (quartz-rock) traverse many rocks, and become broken up into granular forms on weathering ”