338 AZURESTONE FAMILY. Internally it is either glistening or glimmering. The fracture is small and fine-grained uneven. The fragments are angular, and rather blunt-edged, It is feebly translucent on the edges. It is intermediate between hard and semi-hard: it scratches glass, and in some places gives a few sparks with steel. It is easily frangible. It is rather heavy, but in a middling degree. Specific gravity, 2.771, Blvmenbach. 2.767 to 2.945, Hauy. 2.896, Kirwan. 2.761, Brisson. 2.959, Karsten. Chemical Characters. It retains its colour in a low degree of heat: in a higher heat, it melts into a blackish mass; and in a very high heat, it melts into a white enamel. When pounded and calcined, it forms a jelly with acids. It is.deprived of its colour by all the mineral acids: with great rapidity by nitrous acid; less rapidly by mu riatic acid ; and slowest by means of sulphuric acid. Constituent Parts. Silica, - - 46.00 Alumina, - - 14.50 Carbonate of Lime, 2S.OO Sulphate of Lime, 6.50 Oxide of Iron, - 3.00 Water, - - 2.00 100 Klaproth, b. i. s. 196 *. Geognoshc * The older chemists were of opinion, that the beautiful colour of ibis mineral was owing to copper; but it is now known that iron is the only colouring principle it contains.