Sulphates - Anhydrous Sulphates, Glauberite and the Barite Group
The sulphates and the related chromates may be divided into three divisions: (1) Anhydrous Sulphates; (2) Acid and Basic Sulphates; (3) Hydrous Sulphates.
Anhydrous Sulphates
Glauberite
A sulphate of sodium and calcium, Na2Ca(SO4)2. Monoclinic. Crystals thin tabular parallel to base. Basal cleavage. H. = 2.5-3. G. = 2.7-2.885. vitreous luster. Color pale yellow or gray. Slightly saline taste. Fusible (1.5-2), giving yellow flame (sodium). After ignition, givis an alkaline reaction on moistened test paper. Soluble in hydrochloric acid and solution with barium chride gives white precipitate of barium sulphatate. A rare mineral ocurring in the saline deposits, formed by the evaporation of salt lakes.
Barite Group
The barite Group consists of the sulphates of barium, strontim, lead and calcium. They crystallize in the orthorhombic system wth closely related crystals constans and similar habits. The members of the group are as follows:
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