In microscopic characters the andesites present considerable variety; their porphyritic felspars are usually of tabular shape with good crystalline outlines, but often filled with glass enclosures.
The andesites have mostly a porphyritic structure, and the larger felspars and ferro-magnesian minerals are often visible to the naked eye, lying in a finer groundmass, usually crystalline, but sometimes to a large extent vitreous.
Coquimbo) silver is found in the porphyritic conglomerate formation; as I suspect is likewise the case at S.
I believe this last great bed is covered by other nearly similar alternations; but the section is here obscured by a tilt from the nextporphyritic chain, presently to be described.
On its north-eastern flank, and likewise on a few of the summits, the stratified porphyritic conglomerate is inclined N.
Near the point where the river Aconcagua debouches on the basin plain of the same name, at a height of about two thousand three hundred feet above the sea, we meet with the usual purple and greenish porphyritic claystone conglomerate.
Transitions to the porphyritic dolerites and basalts arise by increase in the proportion of this ground-mass.
Many dolerites are porphyritic and carry phenocrysts of olivine, augite and plagioclase felspar (or of one or more of these).
All are even grained, consisting of a mass of crystalline grains formed during one continuous stage of solidification, and no porphyritic crystals appear as in lavas.
They give place as one proceeds east to porphyritic semi-ophitic doleritic rocks of the same genus and to semi-vitreous basic rocks.
On the shores of Wainunu Bay between the Wainunu and Korolevu rivers occur porphyritic basaltic andesites with a considerable amount of glass in the groundmass.
The porphyritic quartz crystals are rounded and about 2 mm.
Displayed in mass in the bed of the river in the same locality, and beneath the submarine tuff just referred to, is a porphyritic basaltic andesite (sp.
At its foot near the river there is exposed at the roadside a rubbly pitchstone formed of a basic glass, inclosing porphyritic crystals of plagioclase, augite, and olivine, which is described on page 313.
These Kandavu rocks had a microfelsitic base, the porphyritic brown hornblende having usually black borders in which a change into epidote was observed.
That the porphyritic basalt represents a later flow around this old andesitic mountain is indicated amongst other things by this absence of tuffs and agglomerates.
On account of the considerable porphyritic development of the plagioclase, the groundmass is relatively diminished, the large phenocrysts occupying about a third of the mass.
The lavas are feldspathic, and of porphyritic structure, and, according to the same authority, of an aggregate thickness of 2500 feet.
The main body of the granite here is of a porphyritic appearance, with large crystals of feldspar; but in the veins it is fine- grained, and without these large crystals.
Next we find, in the same county, that elvans, or straight dikes of porphyritic granite, have cut through the granite and the veins before mentioned, but have not penetrated the Devonian rocks.
Some of the porphyritic rocks above mentioned are highly quartzose, others very feldspathic.
In other parts we find narrow veins of gneiss traversing masses of the granite; and in other parts the granite assumes a porphyritic appearance, containing, imbedded, numerous small nodules of gneiss.
The next rock is a porphyritic horn-stone, and splintery horn-stone.
The apex of the gloomy porphyritic trap is a long spine of the tenderest azure-white, filmy as the finials of Milan Cathedral, and apparently melting into thin air.
A cut road runs to the top of the granite tongue, which faces the westernmost or down-stream outbreaks of the huge porphyritic masses on the other side of the Wady Sadr.
The shales become dense, highly crystalline rocks of a "hornstone" type, with porphyritic developments of silicate minerals.
The sands and sandstones become highly crystalline quartzites, spotted with porphyritic developments of silicates.
We were perplexed by the shallow conical pits in the porphyritic trap, to the east and west of the "Dome Hill;" the ground is too porous for rain cisterns, and the depth is not sufficient for quarrying.
It showed at once a complete change of formation: the sides were painted with clays of variegated colours, crystallized lime and porphyritic conglomerates, tinted mauve-purple as if by manganese.
On the left bank a porphyritic block, up whose side a mule can be ridden, is disposed in a slope of the palest and most languid of greens, broken by piles of black rock so regular as to appear artificial.
At a re-entering angle of the junction, a shallow pit was sunk; the sand became moist and red, and presently it was underlaid by a rubble of porphyritic trap.
From the raised and metalled bank, upon which the Burj stands, we descended to the broad mouth of the Wijh valley, draining the low rolling blue-brown line of porphyritic hillocks on the east.
Olivine and augite are the commonestporphyritic minerals in basalts, the former green or yellowish (and weathering to green or brown serpentine), the latter pitch-black.
Cleavelandite found in the porphyritic granite on the summit of the hill, 212.
The porphyritic beds in Saint Mary's are interesting on account of the distinct appearance of stratification which they display, and Mr. Majendie thinks that an undoubted instance of stratified granite is to be seen near the same spot.
For the information of the Geologist who may visit this spot, we shall state, that in a porphyritic granite on the summit, Mr. W.
Many felsites contain porphyritic crystals of clear quartz in rounded blebs, more or less idiomorphic felspar, and occasionally biotite.
Those which carry porphyritic quartz are known as quartz-felsites; the term soda-felsites has been applied to similar fine-grained rocks rich in soda-felspar.
Passing in full view of these picturesque craters, now mostly covered with trees and brushwood, we begin to ascend, and are soon among theporphyritic range that forms a wall between us and the land of sugar-canes and palms.
It is tetzontli, the porous amygdaloid which abounds among the porphyritic hills, a beautiful building-stone, easily worked, and durable.
The pillars were of porphyritic conglomerate, which had been disintegrated and worn away by wind and rain; while the great masses resting on them, probably of solid porphyry, had been less affected by these influences.
The situation of the mines was picturesque; grand hills of porphyritic rock, and pine-forest everywhere.
For some three hours we rode along among porphyritic mountains, getting higher at every turn, and enjoying the clear bright air.
Masses of euritic and porphyritic rocks intersect the granites, and a distinct formation of porphyries crowns Monte Cinto, Vagliorba, and Pertusato, the highest summits of the Niolo, covering the granite.
Now, towards sunset, we were rapidly gliding along the shore of Isola Rossa, and the slanting rays glowing directly on the porphyritic cliffs gave a rich but mellow intensity to the ruddy hue whence they derive their name.
The surface of the country generally, and more especially in the immediate vicinity of these hills, is strewed with fragments of compact or porphyritic greenstone.
We also saw some porphyritic masses with a basis of greenstone, containing crystals of felspar.
The dikes chiefly consist of a rock, porphyriticwith large crystals of augite; others are formed of a fine-grained and brown- coloured trap.
It is interesting thus to trace the steps by which a compact granular rock becomes converted into a vesicular, pseudo-porphyritic lava, and finally into red scoriae.
The various beds of which the cliffs are composed, as courses of ashlar compose a wall, are of very different degrees of solidity: some are of hard porphyritic or basaltic trap; some of soft Oölitic sandstone or shale.
Such is the appearance which it presents where weathered; but its general aspect is that of a porphyritic trap.
But the objects which chiefly distinguish the architectural remains of Mitla from all other Mexican antiquities are six porphyritic columns, which support the ceiling of a vast saloon.
All the Sierra of Santa Rosa forms a chain of porphyritic mountains and elevations of greater or less elevation, which pass under the general name of Cerros.
It is oval in shape, and hemmed in on all sides by porphyritic mountains and eminences, from which the volcanoes of Popocatepetl and Iztaccihuatl, shoot up beyond the region of eternal snow.
We were stopped by a small circular wall ofporphyritic lava, with a base of pitchstone, which concealed from us the view of the crater.
Montserrat, a solfatara; fine porphyritic lavas with large crystals of feldspar and hornblende near Galloway, according to Mr. Nugent.
These porphyritic caverns, in the Cordilleras of Quito and Peru, bear the Indian name of Machays.
Vauquelin has discovered it even in the porphyritic lavas of Sarcouy in Auvergne.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "porphyritic" in a variety of sentences. We hope that you will now be able to make sentences using this word. Other words: craggy; crystal; crystalline; gravelly; gritty; monolithic; pebbly; rocky; sandy; shingled; stony
