Green augite and hypersthene form a considerable part of these rocks, they may contain also biotite, hornblende and quartz.
The aplites, pegmatites, graphic granites and muscovite granites are usually richest in silica, while with increase of biotite and hornblende, augite and enstatite the analyses show the presence of more magnesia, iron and lime.
The hornblende of granites is usually pale green in section, the augite and enstatite nearly colourless.
On penetrating still deeper, we can detect the constituent parts by the naked eye, and in the Vesuvian currents distinct crystals of augite and leucite become apparent.
A] The dike is 134 feet wide, and consists of a rock which is a compound of felspar and augite (dolerite of some authors).
This name may also be extended to those rocks in which augite is substituted for hornblende (the dolorite of some authors), or to those in which albite replaces common felspar, forming the rock sometimes called Andesite.
It was also remarked, that in the crystalline slags of furnaces, augitic forms were frequent, the hornblendic entirely absent; hence it was conjectured that hornblende might be the result of slow, and augite of rapid cooling.
Brongniart to a rock, having a base of basalt, with more or less distinct crystals of augite disseminated through it.
According to some, this rock is defined to be a mixture of augite or hornblende, and saussurite, a mineral allied to jade.
Chiefly augite--an intimate mixture of augite and felspar with magnetic iron, olivine, &c.
This view was confirmed by the fact, that Mitscherlich and Berthier were able to make augite artificially, but could never succeed in forming hornblende.
As an example of rocks in which augite greatly prevails, basalt may first be mentioned.
Professor Gustavus Rose, to whom I submitted specimens of this dike, finds the rock, which he calls dolerite, to consist of greenish black augite and Labrador felspar, the latter being the most abundant ingredient.
Augite is the predominant mineral, the felspar being in much smaller proportions.
Though typical of basaltic rocks, augite is also an important constituent of many other kinds of igneous rocks, and a rock composed almost wholly of augite is known as augitite.
Typically they consist of pale green or nearly colourlessaugite (omphacite), green hornblende and pink garnet.
The augite is mostly a variety of diopside and is only occasionally idiomorphic.
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.
The chlorites are produced very commonly, but not generally, by the alteration of basic anhydrous silicates, likeaugite and hornblende.
Augite is very similar in composition to hornblende, but contains usually more lime and less alumina and alkali.
Augite and hornblende are typical examples of basic minerals; but augite is, both in its composition and associations, the more basic of the two.
Augite rarely occurs in gneiss; and hence, when we observe a gneiss containing a black mineral which we know is either augite or hornblende, it is pretty safe to call it the latter.
Augite is a common accessory in the more basic syenite; but garnet, tourmaline, and the other accessory minerals, occurring so frequently in gneiss, are almost unknown in syenite.
By the substitution of augite for hornblende, in the description of amphibolite, we get the much rarer, but otherwise very similar, rock, pyroxenite.
When examined in thin sections with the polarizer, augite does not afford the phenomenon of dichroism, which is strongly marked in hornblende.
Columns, pentagonal or heptagonal, crown the tops of hills, and seem rather a composition of hornblende than of augite and feldspar.
A rock of igneous origin, consisting of augite and triclinic feldspar, with grains of magnetic or titanic iron, and also bottle-green particles of olivine frequently disseminated.
Hornblende and augite are two widely distributed minerals, which are so similar in composition and properties that they may be considered together.
The augite builds eumorphic crystals of pale green colour, often zonal and readily weathering.
Their essential minerals in thin section are hornblende of a strong reddish-brown colour; augite purple, pleochroic and rich in titanium, olivine and plagioclase felspar.
They would define the monchiquites as rocks consisting of olivine, augite and analcite; others regard the analcite as secondary, and consider the base as essentially glassy.
New minerals developed about the core of an augite crystal 28 15.
A crystal of augite within the mass of a rock altered in part to form a rim of the minerals hornblende and magnetite.
Such a shower occurred in connection with the eruption of Etna in 1669, and the black augite crystals may to-day be gathered by the handful from the slopes of the Monti Rossi (Fig.
The biotite is brown; the hornblende brown or greenish brown; the augite usually green.
In the older rocks, basalt has often undergone decomposition into melaphyre; and amongst the metamorphic rocks it has been changed into diorite or hornblende rock; the augite having been converted into hornblende.
Phonolite (Clinkstone) is a trachytic rock, composed essentially of sanidine, nepheline, and augite or hornblende.
Crystal of augite with banded walls, and indented by leucite crystals, from the lava of 1794.
Basalt is the most fusible of volcanic rocks, owing to the augite and magnetite it contains, so that it spreads out with a very slight slope when highly fused.
Section of augite crystal from the lava of 1794, with numerous gas cells and delicately banded walls.
Beds of volcanic ash or breccia also frequently occur, and often contain augite crystals.
Vesuvian lava, glass paste with numerous crystals of leucite; others of augite and nepheline porphyritically developed; also small grains of magnetite.
In Minahassa, at the northern extremity, there is a large area of tuffs and agglomerates consisting chiefly of augite andesite, and in this area there are many recent volcanic cones.
The cones themselves are composed largely of acid andesites, but many of the lavas are augite andesites and basalts.
The geognostic phenomena which we are now describing, and which excite the imagination as well as the powers of the intellect, are the result of the action of augite porphyry manifested in its elevating, destroying, and transforming force.
Lime is also one of the component parts of augite and other volcanic and hypogene minerals, and when these decompose is set free, and may then find its way in a state of solution to the sea.
It is a dark green or black stone, composed of augite and felspar, very compact in texture, and of considerable hardness, often found in regular pillars of three or more sides called basaltic columns.
Mica occurs plentifully in some recent trachytes, but is rarely present where augite is in excess.
Crystals of augite have been met with in the scoriae of furnaces, but never those of hornblende; and crystals of augite have been obtained by melting hornblende in a platina crucible; but hornblende itself has not been formed artificially.
One of the varieties of the Trap-rocks, composed of augite and felspar.
When augite (or pyroxene) predominates, lavas are termed basaltic.
Their black augite and yellow green olivine are also easily detected in hand specimens.
Leucite-monchiquites are fine-grained dark rocks consisting of olivine, titaniferous augite and iron oxides, with a glassy ground mass in which small rounded crystals of leucite are scattered.
The commonest ferromagnesian mineral is augite (sometimes rich in soda), with olivine in the more basic varieties.
They are of trachytic appearance, containing phenocysts of sanidine, leucite, augite and biotite.
They may be ophitic, though often they are not, and they usually contain olivine, while theiraugite has distinctly purple shades, and a feeble dichroism.
Many dolerites are porphyritic and carry phenocrysts of olivine, augite and plagioclase felspar (or of one or more of these).
But transition forms are very common, having more or less of the augite remaining, surrounded by newly formed hornblende which at first is rather fibrous and tends to spread outwards through the surrounding felspar.
These rocks consist of augite and plagioclase, with little or no olivine, on a brown, vitreous, interstitial matrix.
Their olivine tends to become serpentinized; their augite changes to chlorite and uralite; their felspars are clouded by formation of zeolites, calcite, sericite and epidote.
The augite is usually brown, but greenish, violet and colourless varieties may occur.
Hornblende when primary is often brown, and may surround augite or be perthitically intergrown with it; original green hornblende probably occurs also, though it is more frequently secondary.
The hypersthene is usually more perfectly idiomorphic and occurs in long prisms, with the pinacoidal planes best developed, while the augite is in stout prisms, usually twinned.
In one andesite the abundance of these remnants of hornblende and also of augite anhedrons in the groundmass may justify the conclusion that this augite andesite is of derivative origin, of the class described by Washington.
On the spurs west of Nisqually Glacier the andesites contain both pyroxenes, the augite being somewhat the more important.
Hypersthene and augite occur alone or together, and are readily distinguished by their different crystallographic habits as well as by their optical properties.
In the more basic phases anhedrons of augite and of olivine appear, and magnetite grains are usually present.
The hypersthene-augite olivine variation, already referred to, doubtless well expresses the chemical composition of the magma, and deserves to be taken as the chief criterion in the classification of the lavas.
Werner first distinguished augite from hornblende; and his proposal to separate them obtained afterwards the sanction of Hauy, Mohs, and other celebrated mineralogists.
It was also found by analysis that augite usually contained more lime, less alumina, and no fluoric acid; which last, though not always found in hornblende, often enters into its composition in minute quantity.
Professor Gustavus Rose, to whom I submitted specimens of this dike, found it to be dolerite, and composed of greenish black augite and Labrador feldspar, the latter being the most abundant ingredient.
This name has usually been extended to all granular mixtures, whether of hornblende and feldspar, or of augite and feldspar.
In addition to these characters, it was remarked as a geological fact, thataugite and hornblende are very rarely associated together in the same rock.
The dike is 134 feet wide, and consists of a rock which is a compound of feldspar and augite (dolerite of some authors).
This view was confirmed by the fact that Mitscherlich and Berthier were able to make augite artificially, but could never succeed in forming hornblende.
It was also remarked that in the crystalline slags of furnaces augitic forms were frequent, the hornblendic entirely absent; hence it was conjectured that hornblende might be the result of slow, and augite of rapid cooling.
In mineral composition they scarcely differ from the lavas of Somma, the rock consisting of a base of leucite and augite, through which large crystals of augite and some of leucite are scattered.
The phenocrysts of plagioclase andaugite inclosed in the altered glass also display extensive alteration, and in the first case are largely replaced by calcite, secondary quartz, and other products.
In the slide are displayed a few small phenocrysts of olivine and pyroxene in a groundmass formed of more or less parallel felspar-lathes, augite granules, magnetite, sometimes in rods, and a little greenish devitrified residual glass.
Those before me show phenocrysts of plagioclase and sometimes of augite in a groundmass displaying a mesh-work of felspar-lathes, prismatic pyroxene, and much interstitial glass.
When present they are generally small and of a pale augite which gives extinctions of 30°.
The occasional small ophitic “plates” of pale augite are not over 1 mm.
The pyroxene phenocrysts, which are of pale brownish-yellow augite giving extinctions of over 30°, do not usually exceed 3 mm.
They display a plexus of felspar-lathes with abundant smoky more or less devitrified glass, the augite granules not being always differentiated.
They are composed of a semi-vitreous hypersthene-augite andesite, containing both augite and rhombic pyroxene, but of an unusual type.
The augite of the groundmass is ophitic or semi-ophitic.
The augitegranules of the groundmass as a rule vary from ·02 to ·04 mm.
The lava of these streams is of similar composition with that of the pinnacle, excepting that the crystals of albite appear to be more comminuted, and the grains of fused augite are absent.
The paste seems to consist of the augite more perfectly fused, or, more probably, merely disturbed in its softened state by the movement of the mass, and mingled with the oxide of iron and with finely comminuted, glassy albite.
A common variety is almost entirely composed of crystals of augite with olivine.
The chief part consists of red decomposing scoriae, associated with various kinds of tuff and yellow argillaceous beds, full of broken crystals, those of augite being particularly large.
The basalt in some parts abounds with large crystals of augite and olivine, and is generally compact.
Augite and olivine are generally present in the Etna lavas, especially the latter mineral.
Specimens of Augite from Etna have been examined by Von Waltershausen and Rammelsberg, with the following results:-- Greenish From From Black.
A small crystal of greenaugite is represented at the bottom of Fig.
The augite in these lavas sometimes occurs in well-formed crystals of a green or brown colour, and often shows the characteristic cleavage very well, especially in the augite crystals of the lava of the Boccarelle del Fuoco, erupted in 1535.
It was found to contain good crystals of augite and olivine, well striated labradorite, and titaniferous iron ore.
A crystal of augite is shown near the bottom of the drawing.
The vitreous matter which occurs in these lavas is principally present in the form of inclosures in the felspar, and, sometimes, the augite and olivine crystals previously described.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "augite" in a variety of sentences. We hope that you will now be able to make sentences using this word.
