Ferriferous Oxide of Cerium. Allanite
- Allanite. Thomson, in Trans. of Royal Society of Edinburgh, vol. VI. p. 371. Bournon Catalogue, 455.
The fortune of war having placed a collection made in Greenland by a persevering German mineralogist, M. Gieseké, in the hands of a British privateer, it was sold in Edinburgh to Mr. Allan, who, upon examining it, found it to contain many rare specimens, particularly of Cryolite and of the substance now before us, which proved to be non-descript. It was placed in the hands of Dr. Thomson, who, having analyzed and described it, gave it a name after its proprietor, not knowing at the time the person to whom it would have been more handsome and more correct to have done that honour.
The primitive form of Allanite, according to Bournon, is a rectangular prism, the height of which is not at present known, and the edges of the base of which are to each other as 12 to 5.6. This prism is generally modified upon its edges; the modifications upon the vertical ones only have been determined.
The following characters are such as Dr. Thomson gives in his paper. The hardness is not sufficient to scratch Feldspar or Quartz, but it scratches Hornblende and Glass. It is brittle, with a conchoidal brilliant fracture; its powder is of a greenish grey colour; in the mass it is black, and, even in thin pieces, opaque. Spec. Grav. from 3.119. to 4.001. Before the blowpipe it froths and melts imperfectly into a brown scoria; it gelatinizes in Nitric Acid. It appears very liable to decay when exposed to the weather, as the external parts of the specimens are much rounded, and the surface of the crystals covered by a thin ochrey crust, the result of its decomposition.
My figures are from the two crystals the Count mentions in the Catalogue of his very scientific collection. The free access I am indulged with to this collection, imposes upon me the pleasing duty of frequently expressing my gratitude to him, for the many favours I hope the public, as well as myself, will be benefited by.
I have given Dr. Thomson’s analysis before, under Cerite, but will repeat it.