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ALBITE

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Originally appearing in Volume V01, Page 512 of the 1911 Encyclopedia Britannica.
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ALBITE , a See also:

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

(L. J. S.) 'ALSO, See also:

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

End of Article: ALBITE

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