Mineralogical chemistry

1883 Journal of the Chemical Society Abstracts  
Aluminium Borate from Siberia. By A. DAMOUR (Conzpt. r e d , 96,(675)(676)(677).-This mineral was found in the pegmatite of the Soktoui mountains, near Adonn-Tohilon,. in Eastern Siberia. It occurs in regular, transparent, almost colourless prisms, with a hardness between thaitl of quartz and that of felspar ; sp. gr. = 3.28. The crystals appear to have no cleavage, and break with a vitreous fracture. I n the blowpipe flame, the mineral becomes white and opaque, and gives the green colomtion
more » ... racteristic of boric wid. It dissolves completely in rnierocosmio salt or in borax, forming a colourless bead, and it turns-blue when moistened with cobalt nitrate solution and strongly heated. The mineral is not attacked by nitric or hydrochloric acid, but after being strongly heated, it dissolves slowly in strong sulphuric acid at 300", solution being facilitated by the addition of a small quantity of hydrofluoric acid. When heated to bright redness, it loses 33 per cent. of its weight, but still contains boric acid. The mineral has the composition B,O" 40.19 ; A1203, 55.03 ; Fe203, 4.08 ; K20, 0.70 = 100.00. The oxygen ratio of A1,0,: B203 is 1 : 1, and the formula of the mineral is therefore Al,O"B,O,. The name Jh-Lrn6re'wite is proposed for the new mineral in honour of its discoverer, M. J6rBmBiew. a previous communication, the author states that a certain constituent of some basalts is not nepheline, as previously supposed, but melilite, or at least something very nearly related to it. In the present paper the details are more fully recorded. The imbedded melilite crystals am short quadratic prisms, four-or eight-sided, with rounded prism faces, but well-formed basal planes. The crystals show not unfrequently cleavage parallel to the basal plane ; they are seldom quite free from inclosures ; colourless or very pale yellow, some of the darker crystalline granules are slightly dichroic. Oblique sections show, in patches, a very fine striation parallel to the basal plane. By means of a mercuric iodide solution, the melilite was isolated from a sample of undecomposed basalt. Sp. gr. = 2.29 ; an analysis gave :-SiO,. A1,O;. Fe203. FeO. CaO. MgO, N+O. K20. HZO. 44.76 7.90 3.16 1-39 87-47 8.60 2-65 0.33 1.42 = 99.68 These numbers show that the ciystalline mineral of sp. gr. 2.99, which is a principal constituent of the basalt from Hochbohl, near Owen, and which was formerly considered as nephiline, is in reality melilite. Following are remarks on the accompanying minerals: and descriptions of the localities (Swabian Alps, N.E. spurs of the Bohemian Forest), and modes of occurrence of the melilite basalts. Nelilite occurs also in nephiline and leucite basalts, as in those of
doi:10.1039/ca8834400719 fatcat:uyxitbq2bbcezeiga3ycnugd44