Allanite and Axinite Composition, Crystallization & Structure

Allanite
A mineral similar to epidote in composition, but containing considerable amounts of the cerium metals, cerium lanthanum and didymium, and sometimes with smaller amounts of yttrium and erbium. Composition complex and widely varying. Monoclinic, habit of crystals often similar to epidote. Commonly massive and in embedded grains. H.= 5.5-6. G. = 3.5-4.2. submentallic to pitchy and resinous luster. Brown to pitch-black color. Fuses at 2.5 with intumescence. Sometimes magnetic after heating. Gealtineses in acids. Occurs as a minor accessory constituent in many igneous rocks. Frequently associated with apidote.

Axinite
Composition. Ca7Al4b2(SIO4)8; with varying amounts of ferrous iron, manganese, magnesium and ferric with the aluminum.

Crystallization. Triclinic. Crystals usually thin with sharp edges but varied in habit (Fig. 330).

Structure. In crystals. Massive, lamellar to granular.

Physical Properties. Pinacoidal cleavage. H. = 6.5-7. G. = 3.27-3.35. vitreous luster. Color clove-brown, gray, agreed, yellow. Transparent to opaque.

Test. Fusible at 2.5-3 with intumescense. When mixed with potassium bisulphate and fluorite and the mixture heated on platinum wire gives a green flame (boron).

Occurrence. Occurs in cavities in granite or debase and especially in the contact zone of these rocks. Notable localities for its occurrence are Bourg d´ Oisans, Isere, France; various points in Switzeland; St. Jus, Cornwall; Obira, Japan; Franklin Furnace, New Jersey, etc.

Name. Derived from a Greek word meaning ax, in allusion to the wedgelike shape of the crystals.

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