Leonard James Spencer and John Smith Flett

Name: 1911 Encyclopædia Britannica
Author: Leonard James Spencer and John Smith Flett

1911 Encyclopædia Britannica (1911)

Summary

“1911 Encyclopædia Britannica”, published in 1911, is a work by Leonard James Spencer and John Smith Flett. It explores elements such as leucite, felspar and mineral.

Quotes from 1911 Encyclopædia Britannica (Leonard James Spencer and John Smith Flett)

Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ One series is essentially igneous (orthogneisses) ; usually they contain pale green pyroxene, a variable amount of felspar, sphene, iron oxides. Quartz, rutile, green hornblende and biotite are often present, while garnet occurs sometimes; hypersthene is rare. They occur along with other types of pyroxene gneiss, hornblende gneiss, amphibolites, &c. In many of them there is no reason to doubt that the scapolite is a primary mineral. Other scapolite gneisses equally metamorphic in aspect and structure appear to be sedimentary rocks. ”

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Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ Those leucite rocks which contain abundant essential plagioclase felspar are known as leucite-tephrites and leucite-basanites. The former consist mainly of plagioclase, leucite and augite, while the latter contain olivine in addition. The leucite is often present in two sets of crystals, both porphyritic and as an ingredient of the ground mass. It is always idiomorphic with rounded outlines. ”

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Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ In the Pyrenees there are extensive outcrops of limestone which are penetrated by igneous rocks described as ophites (varieties of diabase) and lherzolites (peridotites) . At the contacts scacpolite occurs in a great number of places, both in the limestones and in the calcareous shales which accompany them. In some of these rocks large crystals of one of the scapolite minerals (an inch or two in length) occur, usually as octagonal prisms with imperfect terminations. In others the mineral is found in small irregular grains. ”

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Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ Often the scapolite is seen spreading through the felspar, portions being completely replaced, while others are still fresh and unaltered. The felspar does not weather, but remains fresh, and the transformation resembles metamorphism rather than weathering. ”

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Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ The felspar ranges from bytownite to oligoclase, being usually a variety of labradorite; orthoclase is scarce. The augite varies a good deal in character, being green, brown or violet, but aegirine (the dark green pleochroic soda-iron-augite) is seldom present. Among the accessory minerals biotite, brown hornblende, hauyne, iron oxides and apatite are the commonest; melanite and nepheline may also occur. The ground mass of these rocks is only occasionally rich in glass. The leucite-tephrites and leucite-basanites of Vesuvius and Somma are familiar examples of this class of rocks. ”

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Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ Scapolite is commonly a mineral of metamorphic origin, occurring usually in crystalline limestones, but also with pyroxene in schists and gneisses. The long slender prisms abundant in the crystalline limestones and schists in the Pyrenees are known as “dipyre” or “couzeranite.” Large crystals of common scapolite (wernerite) are found in the apatite deposits in the neighbourhood of Bamle near Brevik in Norway, and have resulted from the alteration of the plagioclase felspar of a gabbro. (L. J. S.)
Scapolite Rocks. ”

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Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ Even meionite (the variety richest in soda) occurs in this association, being principally obtained in small crystals lining cavities in ejected blocks of crystalline limestone at Vesuvius and the craters of the Eifel in Germany. Scapolite and wernerite are far more common at the contacts of limestone with intrusive masses. The minerals which accompany them are calcite, epidote, vesuvianite, garnet, wollastonite, diopside and amphibole. The scapolites are colourless, flesh-coloured, grey or greenish ”

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Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ LEUCITE, a rock-forming mineral composed of potassium and aluminium metasilicate KAl (SiO3) 2. Crystals have the form of cubic icositetrahedra {211}, but, as first observed by Sir David Brewster in 1821, they are not optically isotropic, and are therefore pseudo-cubic. ”

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Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ Optical investigations have since proved the crystals to be still more complex in character, and to consist of several orthorhombic or monoclinic individuals, which are optically biaxial and repeatedly twinned, giving rise to twin-lamellae and to striations on the faces. ”

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Leonard James Spencer and John Smith Flett, 1911 Encyclopædia Britannica (1911)

“ It is not a superficial process, but apparently takes place at some depth under pressure, and probably through the operation of solutions or vapours containing chlorides. The basic soda-lime felspars (labradorite to anorthite) are those which undergo this type of alteration. ”

Leonard James Spencer and John Smith Flett

Summary

Quotes from 1911 Encyclopædia Britannica (Leonard James Spencer and John Smith Flett)

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