APOPHYLLITE, a crystallised mineral, whose fundamental form is the square prism, fig. 1. Its most general modification is obtained by supposing the angles of fig. 1 cut off, so as to give rise to a plane triangular surface, as is seen at a in fig. 2 ; these faces a, from the plane cutting deeper into the original crystal till they intersect each other, frequently lose their triangular form, and of course, at the same time, the taco I' again becomes a square, and the prism will be terminated by the form seen in fig. 3. On account of these modifications, Apophyllite sometimes assumes the form in fig. 4.
The inclination of P on a is 120 5' L on a in 12S° 20' PI a on a is 104° 18' The structure of this mineral is lamellar, and admits of cleavage in directions parallel to the sides of the regular prism, but most readily in the perpendicular to its axis. Its colour is white or gray, some
times tinged green or red. It possesses various degrees of transparency, and occurs even opaque. In hardness it approaches nearly to Apatite ; and its density varies from 2.3 to Before the blow-pipe it forms a white glass. Its chemical constitution is stated as follows : 8 (Ca + 3 Si) + (K + 6 Si) + 16 Aq and the mineral is therefore an hydrated silicate of potash and lime.
Apophyllite has been found in the mines of magnetic iron-ore of Sweden and Norway ; in the lead-mines of the Harz Mountains ; also in the cavities of several basaltic rocks, at Marienberg in Bohemia ; at Foesa in the Tyrol ; in the Isle of Skye, &e. In the basalts it is usually accompanied by Analcimc and Slilbile.
This mineral is sometimes called Tesaclile. Albin is a white variety.