Hydrous Phodphates – Vivianite, Scorodite & Wavellite Composition

Vivianite
Hydrous ferrous phosphate, Fe₃P₂O₈8H₂O. Monoclinic. Prismatic crystals, vertically striated; often in radiating groups; at times fibrous or eartly. Perfec pinacoidal cleavage. H. = 1.5-2. G. = 2.58-2.68. Vitreous to pearly luster. Colorless when un altered. Transparent when fresh to opaque on exposure. Fusible at 2-2.5 to a magnetic globule. Nitric acid solution added to an excess of ammonium moybdate solution gives yellow precipitate (test for phosphate). Water in C. T. A rare mineral of secodary origin, associated with pyrrhotite, pyrite, limonite and other iton minerals.

Erythrite or Cobalt Bloom, Co₃As₂O₈8H₂O, is a rare secondary minerals which occurs as an alteration product of cobalt arsenides. It is usually pulverunlent in structure and crimson to pink in color. Annabergite or Nickel Bloom, Ni₃As₂O₈8H₂O, is a similar nickel compound. It is light green in color.

Scorodite
A hydrous ferric arsenate, FeAsO₄.2H₂O. Orthorhombic, usually in pyramidal crystals, resembling octahedrons; also prismatic. Crystals in irregular groups. Also earthy. H = 3.5-4. G. = 3.1-3.3. Vitreuos luster. Pale green to liver-brown in color. Translucent. Fusible at 2-2.5. Magnetic when heated in R. F. Heated intensely with splinder of charcoal in C. T. gives arsenical mirror. Water in C. T. In hydrochloric acid reacts for ferric iron. Occurs in oxidized portions of metallic veins with arsenopyrite and other iron minerals.

Wavellite
A hydrous aluminum pohosphate, (AlOH)₃(PO₄)2. 5H₂O. orthorhombic, crystals rare. Usually in radiating globular agregates. Good cleavage. H. = 3-4. G. = 2.33. vitreous luster. Colo white, yellow, green and brown. Traslucent. Infusible.Insoluble. Decomposed by fusion with sodium carbonate and dissolved in nitric acid gives yellow precipitate (tes for phosphoric acid) when solution is added to excess of ammonium molybdate. Moistened with cobalt, and then ignited assumes a blue color (aluminum). A rare mineral.