A finegrained rock, flintlike in fracture, consisting essentially of orthoclase feldspar with occasional grains of quartz.
A mineral of the feldspar group, like orthoclase or common feldspar in composition, but triclinic in form.
A granular, crystalline, ingeous rock composed of orthoclase and hornblende, the latter often replaced or accompanied by pyroxene or mica.
These larger felspars have no crystalline outlines and consist of orthoclase or microcline surrounded by borders of white oligoclase.
The felspar of the granulites is mostly orthoclase or cryptoperthite; microcline, oligoclase and albite are also common.
Under the microscope the felspar is mainly orthoclase with perthite or microcline, while a small amount of plagioclase (ranging from oligoclase to albite) is practically never absent.
Orthoclase and quartz, if present, are last to separate out, and fill the spaces between the other minerals; often they interpenetrate to form micropegmatite.
Orthoclase is rarely entirely absent, and when it is fairly common the rock becomes a tonalite; in this way a transition is furnished between diorites and granites.
Hornblende-gneisses are usually darker in colour and less fissile than mica-gneisses; they contain more plagioclase, less orthoclase and microcline, and more sphene and epidote.
Although with wide variation in chemical composition, the feldspars are yet broadly divided into two classes; the one striated, and the other an unstriated potash or orthoclase variety.
The composition of the magma will thereby change, and the mass will finally solidify to a mixture of orthoclase and silica, or orthoclase and potassium aluminate, according to the initial composition.
If the initial composition of the magma is represented by a point between the two eutectic points, orthoclase will separate first.
This curve would represent the conditions under which orthoclase is in equilibrium with the molten magma.
Felspar if present may be orthoclase and oligoclase.
This change may be illustrated by quoting the analysis of a kaolin clay formed by the disintegration of orthoclase felspar.
In many of their structural peculiarities they closely simulate the rhyolites, from which they differ in containing less potash and more soda, and in consequence less orthoclase felspar and more plagioclase.
Of late years, magnificent crystals have been obtained from Pike's Peak, Colorado, where it is found associated with smoky quartz, orthoclase and albite in a coarse granite or pegmatite.
Aventurine and moonstone varieties occur, though these special appearances are more usually displayed by the oligoclase and orthoclase felspars respectively.
The hornblende- and mica-andesites have groundmasses composed mainly of acid plagioclase with little orthoclase or glassy base (pilotaxitic groundmass).
These dolerites are cut through by intrusive syenite, and this syenite, in its turn, is again cut and penetrated by feldspar porphyry, the base of which consists of petrosilex, or a mixture of orthoclase and quartz.
Miascite is one of the varieties of syenite most frequently spoken of; it is composed chiefly of orthoclase and nepheline, with hornblende and quartz as occasional accessory minerals.
Orthoclase is orthoclastic and monoclinic; all the other feldspars are plagioclastic and triclinic.
Among the applications of felspar is that of pure orthoclase in the manufacture of artificial teeth.
In England the material employed is mostly orthoclase from Scandinavia, often known as "Swedish spar.
Mallard suggested that all felspars are really asymmetric, and that orthoclase presents only a pseudo-monosymmetric habit, due to twinning.
The turbidity of orthoclaseis usually due to partial kaolinization.
Examples of substances exhibiting these three kinds of dispersion are borax, orthoclase and gypsum respectively.
At the same time orthoclase and microcline are both potassium felspars; yet the former crystallizes in the monoclinic, and the latter in the triclinic system.
That rocks consisting of orthoclase, of orthoclase and hornblende, or of orthoclase and mica, i.
The orthoclase is sometimes replaced in part by triclinic species, especially albite and oligoclase.
Orthoclase crystallizes in the monoclinic system, and all the other feldspars in the triclinic system.
In texture, the granites vary from perfectly compact varieties, approaching petrosilex, to those which are so coarsely crystalline that single crystals of orthoclasemeasure several inches in length.
In other words, the distinction of orthoclase from the basic or triclinic feldspars is important and comparatively easy, while the distinction of the different basic feldspars from each other is both unimportant and difficult.
The general physical characters, including the cleavage, are well exhibited in the common species, orthoclase (specimen 22).
Orthoclase is the predominant constituent in all typical gneiss, usually forming at least one-half of the rock.
Quartz and orthoclase are the only essential constituents of gneiss; and when these alone are present, we have the variety known as binary gneiss.
The orthoclase may, however, be replaced to a greater or less extent by albite, or even by oligoclase.
Orthoclase is always the predominant ingredient; and, except when there is much hornblende present, usually determines the color of the granite.
The orthoclase in syenite is more frequently replaced by plagioclase than it is in gneiss.
Defn: A variety of orthoclase feldspar common in certain eruptive rocks, as trachyte; -- called also glassy feldspar.
Defn: A mineral of the feldspar group, like orthoclase or common feldspar in composition, but triclinic in form.
Defn: A finegrained rock, flintlike in fracture, consisting essentially of orthoclase feldspar with occasional grains of quartz.
Ocellar structure is common; the ocelli consist mainly of orthoclase and quartz, and may be a quarter of an inch in diameter.
The plagioclase occurs as small rectangular crystals; orthoclase may have similar shapes or may be fibrous and grouped in sheaflike aggregates which are narrow in the middle and spread out towards both ends.
Granite is a mixture of quartz, felspar, and mica in variable proportions, and the quality of the soil it yields depends on whether the variety of felspar present be orthoclase or albite.
Those yielded by orthoclase must generally abound in potash, while albite and labradorite, containing little or none of that element, must produce soils in which it is deficient.
The felspars are orthoclase and plagioclase; the former is much decomposed, while the plagioclase frequently remains clear, and exhibits well its twin striation.
In the large quarry there is a very coarsely crystalline variety containing large flat plates of ilmenite, and here also may be found some light-coloured veins in which orthoclase is the predominant felspar.
The felspar is of two kinds, orthoclase and plagioclase, the former is very turbid and decomposed, while the plagioclase is clear, and retains its usual optical characters.
Amelia Court House, Virginia, is another locality whence come pieces either of orthoclase or oligoclase exhibiting this property.
Trachyte, on the other hand, is the least fusible owing to the presence of orthoclase felspar, or quartz; so that the volcanic domes formed of this material stand at a higher angle from the horizon than those of basaltic cones.
Both the quartz and orthoclase contain dust inclusions and crystallites, while the evidences of shearing and crushing are abundant.
Between these bands of orthoclase and the neighboring amphibolite are narrow bands of schist [2] One hundred feet south of the above point is a second dike having a similar strike and dip and a width of eighteen feet.
A soft extremely fine grained gray rock, with a well developed schistose structure, carrying much magnetite, plagioclase, orthoclaseand their alteration products.
In the hand specimen it is an apparently pure orthoclase but in the thin section small scattered quartz grains are observed; as well as the alteration products, Kaolin and sericite.
The felspar ranges from bytownite to oligoclase, being usually a variety of labradorite; orthoclase is scarce.
The rocks in which orthoclase (or sanidine) is present in considerable amount are leucite-trachytes, leucite-phonolites and leucitophyres.
In ordinary red granite it is easy to distinguish large pieces of orthoclase mixed with dark semi-transparent quartz and flexible laminæ of mica.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "orthoclase" in a variety of sentences. We hope that you will now be able to make sentences using this word.
