The commonest accessories are sphene, zircon, iron ores and apatite. Cancrinite occurs in several nepheline-syenites; in others there is fluor-spar or melanite garnet. Small amounts of primary calcite also occur in some nepheline-syenites. A great number of interesting and rare minerals have been recorded from these rocks and the pegmatite veins which intersect them. Among these we may mention eudialyte, eukolite, mosandrite, rinkite, johnstrupite, lavenite, hiortdahlite, perofskite and lamprophyllite. Many of these contain fluorine and the rare earths.
Nepheline-syenites are rare rocks ; there is only one occurrence in Great Britain and one each in France and Portugal. They are known also in Bohemia and in several places in Norway, Sweden and Finland. In America these rocks have been found in Texas, Arkansas and Massachussetts, also in Ontario, British Columbia and Brazil. South Africa, Madagascar, India, New South Wales, Tasmania, Timor and Turkestan are other localities for the rocks of this series. They exhibit also a remarkable individuality, as each occurrence has its own special features ; moreover a variety of types characterizes each occurrence, as these rockS are very variable. For these reasons, together with the numerous rare minerals they contain, they have attracted a great deal of at tention from petrographers.
Many types of nepheline-syenite have received designations derived from the localities in which they were discovered. The laurdalites (from Laurdal in Norway) are grey or pinkish, and in many ways closely resemble the laurvikites of southern Norway, with which they occur. The 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 recog nized according to their mineral composition. Examples of the first-named occur in southern Norway with the laurdalites; they contain aegirine and black mica. At Alno Island in the Gulf of Bothnia (Sweden) similar rocks are found bearing enclosures of altered limestone with wollastonite and scapolite. In Tran sylvania there is a well-known rock of this group, very rich in microcline, blue sodalite and cancrinite. It contains also ortho clase, nepheline, biotite, aegirine, acmite, etc. 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 can crinite. Hornblende-foyaites 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, Sao 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 Litch field, 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 con tains hardly any orthoclase, but only albite felspar. Nepheline is very abundant and there is also cancrinite, sodalite, scapolite, cal cite, 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 con tain also microcline-perthite, aegirine, arfvedsonite and eudialyte. Cancrinite-syenite, with a large percentage of cancrinite, has been described from Dalekarlia (Sweden) and from Finland.
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 5o 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.