ALBITE  , a

mineral of the felspar group, belonging to the division of the plagioclases (q.v.) . It is a sodium and aluminium silicate, NaAlSi3Os, and crystallizes in the anorthic system . Like all the felspars it possesses two cleavages, one perfect and the other less so, which are here inclined at an angle of 86° 24' . On the more perfect cleavage, which is parallel to the basal plane (P), is a system of fine striations, parallel to the second cleavage (M), due to twinning according to the albite law " (figs. r and 2) . The hard- ness is 6, and the specific gravity 2.63 . The colour is usually pure white, hence the name (from the Lat. albus) for the species . Albite forms an essential constituent of many acidic igneous and crystalline rocks; in granites, diorites, andesites, &c., it occurs as a primary mineral, whilst in crystalline schists, phyllites and crystalline limestones it is of secondary (metamorphic) origin . The beautifully developed crystals so abundant in crystal-lined crevices of Alpine granites and gneisses have been deposited, with other minerals, from solution; the crystals lining veins in the slates of Tintagel in Cornwall have the same origin . Several varieties of albite are distinguished, of which the following may be here specially mentioned . Pericline (from the Gr. trepu<Xt -I r, " sloping ") is the name given to large opaque white crystals from the chlorite-schists of the Alps; they are tabular parallel to the direction of perfect cleavage and are twinned according to the " pericline law." Peristerite (from the Gr . 7repurTEpa, a dove) is characterized by a beautiful bluish sheen, somewhat resembling that seen on the neck of a pigeon; it is found mainly in Ontario . Aventurine and moonstone varieties occur, though these special appearances are more usually displayed by the oligoclase and orthoclase felspars respectively .

(L . J . S.) 'ALSO,

JOSEPH, a Spanish Jewish theologian of the ,5th century . He was author of a very popular book on the philosophy of Judaism, entitled 'Iqqarim or Fundamentals . Maimonides in the 12th century had formulated the principles of Judaism in thirteen articles; Albo reduced them to three: (i) The Existence of God, (ii) Revelation and (iii) Divine Retribution . Albo set the example of minimizing Messianism in the formulation of Jewish beliefs . Though he fully maintained the Mosaic author-ship of the Law and the binding force of tradition, he discriminated between the essential and the non-essential in the practices and beliefs of Judaism . An English translation of the 'Iqqarim appeared in the Hebrew Review, vols. i.-iii .