It may be obtained in at least two different forms, one isomorphous with NaCl.
The artificial preparation of minerals, especially of apatite and isomorphous minerals and of crystalline oxides, was another subject in which he made many experiments.
Hedenbergite, or calcium iron pyroxene, is a black mineral closely allied to diopside and, owing to the isomorphous replacement of iron by magnesium, there is no sharp line of division between them.
Ferrous sulphate forms large green crystals belonging to the monoclinic system; rhombic crystals, isomorphous with zinc sulphate, are obtained by inoculating a solution with a crystal of zinc sulphate, and triclinic crystals of the formula FeSO 4.5H 2 O by inoculating with copper sulphate.
It forms double salts such as MgTh(NO 3) 6.8H 2 O, which are isomorphous with the corresponding cerium compounds.
Wollaston in the angles of the rhombohedra of the carbonates isomorphous with calc-spar, he observed that the angle in the case of calc-spar varied with the temperature.
Chromous sulphate, CrS04 7H 2 0, isomorphous with ferrous sulphate, results on dissolving the metal in dilute sulphuric acid or, better, by dissolving chromous acetate in dilute sulphuric acid, when it separates in blue crystals on cooling the solution.
The crystals are isomorphous with mispickel, but only rarely are they distinctly developed and simple (fig.).
Other pairs of isomorphous argentiferous minerals are: the cubic polybasite, 9Ag2S Sb2S3, and pearceite, 9Ag2S As2S3; and the germanium minerals argyrodite, 4Ag 2 S GeS2, and canfieldite, 4Ag 2 S (Sn, Ge) S2.
Rutile assumes tetragonal forms isomorphous with cassiterite, SnO 2 (and also zircon, ZrSiO 4); anatase is also tetragonal, and brookite or thorhombic. Rutile is the most stable and anatase the least, a character reflected in the decrease in density from rutile (4.2) and brookite (4.0) to anatase (3.9).