Quartzite

“ The rocks used for making spear-heads are black basalt and fine granular quartzite. I have not seen any made of quartz, which may be easily accounted for. The quartzite of which the spear-heads are made is almost like jasper; it is tough, and when properly fractured gives a fine even edge, which quartz does not, and it is not brittle. The natives had their choice of rocks in the north, and invariably they chose the best for their purposes. If they had not had quartzite, they would, like many of the tribes of West Australia, have used quartz. ”

“ 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. ”

“ The rock fractures conchoidally through both the grains and cement, so the broken surface, unlike that of sandstone, is smooth and may even be glassy like quartz.
Color depends upon the amount and kind of impurities present. A quartzite that is all quartz is white or gray, but iron or other elements may change the color to shades of purple, yellow, brown, or red. Quartzite is a very resistant, hard rock and cannot be scratched by a knife.
Quartzite is abundant as boulders and pebbles in glacial drift of Illinois, having been brought into the state during the “Ice Age.” ”

“ The quartzite, on the other hand, is the formation of the ridges, though it outcrops at a few points in the plain. (Compare Plates II and XXXVII.) The striking topographic contrasts between the plains and the ridges is thus seen to be closely related to the rock formations involved. It is the hard and resistant quartzite which forms the ridges, and the less resistant sandstone which forms the lowlands about them. ”

“ 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. ”

“ Some quartzites are almost pure quartz, but others contain impurities of clay, lime or iron, which were in the original sandstone. These alter in the metamorphism to such accessory minerals as feldspar, mica, cyanite, magnetite, hematite, calcite, graphite, etc. The color of quartzite when pure is white, but may be altered to red, yellow, or green by the presence of these accessory minerals.
On account of the difficulty of working the quartzites, they are not much used in building, though they are very durable. When crushed they often make excellent road ballast, or filling for concrete work. ”

“ Some of this output, in which may be found fragments of quartz and quartzitic schist, of mica, hornblende, and chloritic schists and slates, of granitic gneiss and gneissose granite, porphyry, diabase, diorite, and quartz (quartzite) , is probably extra-territorial, having been washed in at a time when a more extensive foreign water had access to the region; but there is enough of outcrop to show that most, and perhaps all, of the types here indicated are really a part of the tract. ”

“ They, however, often show wavy extinction and even cracks, but not to a greater degree than the grains in the massive quartzite; for in the latter the full stress of the pressure has been borne by the grains in full touch, not separated by a plastic matrix, as are the grains of quartz in the argillaceous layers. In the matrix of the schist are numerous small flakes of muscovite, arranged with their longer axes in a common direction, much finely crystalline quartz, and a good deal of iron oxide. ”

“ The bedding has been disturbed, so that the strata lie at angles approaching the vertical, and have been broken, and minutely penetrated by quartzose injections, both along and across the bedding planes. Foliation and schistosity have been induced, and the arrangement of the chemical constituents has been altered so that new minerals are formed. The impure cherty limestone is changed to hornblendic schists, the impure sandstone and quartzite to garnet-bearing quartzose gneisses, and the cherty iron ores to a gneissic rock consisting of layers of quartz and specular iron. ”

“ Besides the crystalline quartz rock we find close-grained and at least partly non-crystalline varieties, such as hornstone and flint. Sandstones most commonly consist of grains of quartz cemented by some other mineral, or by silica itself; in the latter case the siliceous sandstone frequently passes insensibly into true quartzite. The loose sand so well known to common life is prevalently composed of quartz grains, whose hardness and resistance to weathering enables them to survive longest the soil-forming agencies. ”

“ An aberrant form is elliptical in section at the middle, round or nearly so at the ends, the sides expanding rapidly from end to middle by 124 double curves. It is represented by figure 146 (ferruginous quartz, from Kanawha valley, West Virginia) , and by a specimen of quartzite from Union county, Mississippi. ”

“ The great series of quartzites were derived from the complete decomposition of quartz-bearing rocks, and involved the almost complete separation of the quartz grains from other constituents, while the thick beds of shale arose from the complementary clayey products of decomposition from which most of the basic oxides had been removed by carbonation. ”

“ The microscopic characters of the quartz in sandstone commonly attest its origin. The minute liquid inclusions, with moving bubbles, that arise in the quartz of igneous and metamorphosed rocks, are easily seen in sections of sandstone. In some quartzites, these inclusions run in continuous bands from grain to grain, and have clearly arisen since the detritus was cemented. But in ordinary sandstones the inclusions in one grain have no relation to those in its neighbours. The felspars, moreover, of igneous rocks are commonly found, as rolled fragments, in sandstone. ”

“ Only rarely, however, does metamorphism produce much difference in the chemical composition of the rocks affected. Sandstones become quartzite’s and quartz schists, limestones are converted into marbles, granite passes into gneiss, and so on, without their bulk composition being greatly modified. From all that we know it seems established that however great the heat and pressure to which metamorphic rocks have been exposed they have very rarely been melted or reduced to the liquid state. ”

“ If the pebbles embedded in the matrix are sharp and angular, freshly broken and not worn, the rock is called breccia and is generally found near the place where the fragments originated. Conglomerate or breccia may be made up of any type of rock or mineral, most commonly durable material such as chert, quartz, quartzite, granite, and gneiss.
In Illinois, conglomerates commonly are found at the base of sandstone formations and as beds in the lower “Coal Measures.” They also are found in some gravel deposits. ”

“ Quartz crystallizes in the rhombohedral system, and many varieties are found massive and compact. The cleavage is indistinct but can sometimes be found by plunging a heated crystal into cold water. The hardness of quartz is 7; specific gravity 2.5 to 2.8, the purest kinds being 2.65; the lustre is vitreous to resinous, and fracture conchoidal.
Quartz is tough, brittle, and feels cold; it becomes positively electric by rubbing, shows phosphorescence in the dark, and gives sparks if struck with another piece of quartz or with steel. ”

“ 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 ”

“ Quartz is composed of the two elements occurring the most abundantly in the earth's crust, silicon and oxygen, both non-metals. As already indicated, the most common representative of the mineral substance is the sand of the soil. The sand grains are generally so eroded by the atmosphere and surface waters as to show little of the true quartz structure. A typical specimen of quartz, commonly known as "rock crystal," clear, transparent and approximately perfect in form, is not difficult to obtain for study. ”

“ We know that quartz requires a higher temperature to melt it than does either the feldspar or the mica, and so, had the granite been formed as are regular volcanic rocks in the ordinary way of igneous fusion, we should certainly have found that the quartz would have crystallized before either the feldspar or the mica, and it would have been seen in definite crystalline form, and its crystals would have interfered with and penetrated those of the other mineral constituents of the rock. ”

“ Opaque dark green, brown, or black Picotite or chrome spinel: Translucent dark yellow-brown or green-brown QUARTZ
(INCLUDES ROCK CRYSTAL, AMETHYST, AND CITRINE)
Few gemstones can compete with quartz for variety of color. Having a hardness of 7 and occurring in many beautiful varieties, only the relative abundance of quartz prevents the species from attaining top rank among gemstones.
The two kinds of quartz, crystalline and cryptocrystalline (fine-grained) quartz, occur in all kinds of mineral deposits throughout the world. Much of this material is suitable for cutting gems. ”

“ 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. ”

“ It offers another example of the striking resemblance between quartz rock and the secondary sandstones; an agreement much more remarkable than that of the mica slate which generally accompanies it, with the slate clay which is the associate of those sandstones. It would seem as if the quartz rock from its greater simplicity of materials, a simplicity less liable to chemical changes, had undergone fewer alterations during the progress of time and of those actions by which its present form was produced, than the more compound schist with which it was originally associated. ”

“ Sometimes the mineral is imbedded in limestone, in the form of nodules, thus indicating their original connexion with it.
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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. ”

“ 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. ”

“ It has been noticed as somewhat remarkable that the quartz in granite should have been usually the last mineral to crystallize, although it is that one which is the most difficult to fuse, and which would therefore naturally be expected to have been solidified before the feldspar and the mica. But it has been shown that, when quartz is in combination with other mineral substances, it is often as readily fusible as they are ”

“ It will be noticed at once that it bears a considerable amount of evidence of what is called "current-bedding," that is to say, that the strata, instead of being regularly deposited, exhibit series of wedge-shaped masses, which are constantly thinning out.
Sand and quartz are of the same chemical composition, and in all probability the sand of which every sandstone in existence is composed, appeared on this earth in its first solid form in the shape of quartz. Now quartz is a comparatively heavy mineral, so also, therefore, will sand be. ”

“ Here is nobly born quartz living with a green mineral, called epidote; and they are immense friends. Now, you see, a comparatively large and strong quartz-crystal, and a very weak and slender little one of epidote, have begun to grow, close by each other, and sloping unluckily towards each other, so that at last they meet. They cannot go on growing together; the quartz crystal is five times as thick, and more than twenty times as strong [Footnote: Quartz is not much harder than epidote; the strength is only supposed to be in some proportion to the squares of the diameters.] ”