Wiikite.
[75]—A mineral of very complex composition, for which no definite formula can be assigned. Its chemical nature may be understood from the following analytical data:
Columbic and tantalic anhydrides = 16·0; Dioxides of titanium and zirconium = 23·4; Silica = 17·0; Ceria = 2·5; Yttria = 7·6; Scandia = 1·2; Thoria = 5·5; Ferrous oxide = 15·5; Uranic oxide = 3·6; water (and gas) = 5·8 per cent.
[75] Crookes, Phil. Trans. 1908, A, 209, 15.
Traces of lime, magnesia, stannic oxide and sulphur are also present.
The mineral is infusible; on heating, helium, sulphuretted hydrogen and water vapour are given off, and a white sublimate is formed. The evolution of gas is almost explosive, the mineral breaking with a curious fracture.
It is black and perfectly amorphous, showing no trace of crystalline structure or action on polarised light. Hardness, 6; sp. gr. 4·85.
Wiikite is partially attacked by acids, readily by fused potassium bisulphate. It is radioactive.
The mineral was found with monazite in a felspar quarry at Impilaks, Lake Ladoga, Finland. It is important as the source of scandium used by Sir William Crookes in his investigations of that element; some specimens of the mineral contain over 1 per cent. of the oxide (see [p. 44]).
The following related minerals, of which descriptions are given in the alphabetical [list], are to be included here: