Page:EB1911 - Volume 19.djvu/402

 foyaites include the greater number of known nepheline-syenites and are called after Foya in the Serra de Monchique (southern Portugal), from which they were first described. They are grey, green or reddish, and mostly of massive structure with preponderating potash felspar, some nepheline, and a variable (often small) amount of femic minerals. Pyroxene-, hornblende- and biotite-foyaites have been recognized according to their mineral composition. Examples of the first-named occur in southern Norway with the laurdalites; they contain aegirine and black mica. At Alnö Island in the Gulf of Bothnia (Sweden) similar rocks are found bearing enclosures or altered limestone with wollastonite and scapolite. In Siebenburgen (Hungary) there is a well-known rock of this group, very rich in microcline, blue sodalite and cancrinite. It contains also orthoclase, nepheline, biotite, aegirine, acmite, &c. To this type the name ditroite has been given from the place where it occurs (Ditro). Pyroxene-foyaite has been described also from Pouzac in the Pyrenees (S. France). Mica-foyaite is not very common, but is known at Miask in the Ural Mountains (miaskite), where it is coarse-grained, and contains black mica, sodalite and cancrinite. The hornblende-foyaites are usually brown or blue, and intensely dichroic, but may contain also biotite or augite. Rocks of this class occur in Brazil (Serra de Tingua) containing sodalite and often much augite, in the western Sahara and Cape Verde Islands; also at Zwarte Koppies in the Transvaal, Madagascar, São Paulo (in Brazil), Paisano Pass (West Texas) and Montreal, Canada. The rock of Salem, Mass., U.S.A., is a mica-foyaite rich in albite and aegirine; it accompanies granite and essexite.

Litchfieldite is another well-marked type of nepheline-syenite, in which albite is the dominant felspar. It is named after Litchfield, Maine, U.S.A., where it occurs in scattered blocks. Biotite, cancrinite and sodalite are characteristic of this rock. A similar nepheline-syenite is known from Hastings Co., Ontario, and contains hardly any orthoclase, but only albite felspar. Nepheline is very abundant and there is also cancrinite, sodalite, scapolite, calcite, biotite and hornblende. The lujaurites are distinguished from the rocks above described by their dark colour, which is due to the abundance of minerals such as augite, aegirine, arfvedsonite and other kinds of amphibole. Typical examples are known near Lujaur on the White Sea, where they occur with umptekites and other very peculiar rocks. Other localities for this group are at Julianehaab in Greenland (with sodalite-syenite); at their margins they contain pseudomorphs after leucite. The lujaurites frequently have a parallel-banding or gneissose structure.

Sodalite-syenites in which sodalite very largely or completely takes the place of nepheline occur in Greenland, where they contain also microcline-perthite, aegirine, arfvedsonite and eudialyte. Cancrinite-syenite, with a large percentage of cancrinite, has been described from Dalekarlia (Sweden) and from Finland. We may also mention urtite from Lujaur Urt on the White Sea, which consists very largely of nepheline, with aegirine and apatite, but no felspar. Jacupirangite (from Jacupiranga in Brazil) is a blackish rock composed of titaniferous augite, magnetite, ilmenite, perofskite and nepheline, with secondary biotite.

The chemical peculiarities of the nepheline-syenites are well marked, as will be seen from the following analyses. They are exceedingly rich in alkalis and in alumina (hence the abundance of felspathoids and alkali felspars) with silica varying from 50 to 56%, while lime, magnesia and iron are never present in great quantity, though somewhat more variable than the other components. As a group, also, these rocks have a low specific gravity.

 NEPHELINITES. The group of effusive rocks which contains nepheline with plagioclase felspar is subdivided into nepheline-tephrites and nepheline-basanites, while those which contain nepheline but not felspar are nephelinites and nepheline-basalts. The tephrites differ from the basanites in the absence of olivine, and the same distinction subsists between the nephelinites and nepheline-basalts.

In their essential and accessory minerals, appearance and structure, these rocks have much in common, and they tend to occur in a natural association as basic rocks comparatively rich in alkalis and alumina. The nephelinites and tephrites are rather

closely linked to the phonolites and pass into them by various gradations. They are usually richer in alkalis and silica and contain less iron, lime and magnesia than the basanites and nepheline-basalts, a difference which finds expression in the presence of olivine and the smaller amount of felspars and felspathoids in the latter.

The nepheline is colourless and transparent when fresh, often in six-sided prisms, but also as irregular interstitial masses filling the spaces between the other minerals, and hard to identify owing to its low double refraction and frequent decomposition. Leucite appears in some tephrites; haüyne is more frequent as small dodecahedra often filled with black inclusions. The augite varies a good deal, being bright green or dark green (aegirine) and rich in soda in some tephrites and nephelinites, while in basanites and basalts it is often brown “basaltic” augite or purple “titaniferous” augite. It has often good crystalline form, and occurs as eight-sided monoclinic prisms, but the soda augites may be of late crystallization and form mossy or irregular growths in the matrix. Brown hornblende is much less common, and a red biotite is very characteristic of certain nephelinites. Of the felspars, labradorite is probably the most common, with more acid varieties of plagioclase. Sanidine is by no means absent, but may be considered as an accessory. The olivine presents no peculiarities. Melilite, perofskite, pseudobrookite, melanite garnet, iron oxides, apatite and chromite are occasionally met with.

 NEPHEW, the son of a brother or sister. The word is adapted from Fr. neveu, Lat. nepos (originally “grandson” or “descendant”). The O. Eng. nefa survived in the form neve till the 15th century; this represents the Teutonic branch, cf. Ger. Neffe, Dutch neef; the ultimate root is seen in the cognate Gr. , “descendants,”  , “kinsman,” and Sans. napāt, napt, “descendants” or “descendant.” The correlative “niece,” the daughter of a brother or sister, is from Fr. nièce, Lat. neptis, the feminine form of nepos; the O. Eng. word was nift, cf. Ger. Nichte. A euphemistic use of “nephew” is that of the natural son of a pope, cardinal or other ecclesiastic; and from the practice of granting preferments to such children the word “nepotism” is used of any favouritism shown in finding positions for a man’s family.  NEPI (anc. Nepet or Nepete), a town and episcopal see of Italy, in the province of Rome, 7 m. S.W. of the town of Civita Castellana, 738 ft. above sea-level. Pop. (1901) 2973. The site, surrounded by ravines and accessible only on the W., is naturally strong and characteristic of an Etruscan town; on this side there is a considerable fragment of the ancient Etruscan wall, built of rectangular blocks of tufa (whether the rest of the site was protected by walls is uncertain), and a ruined castle, erected by Antonio da Sangallo the elder in 1499, for Pope Alexander VI., and restored by Pope Paul III. The municipio (town hall) is from the designs of Vignola, and contains some ancient