Year: 1916
Type: book
Abstract: Alunite is a hydrous sulphate of potash and alumina which may be represented!by the following formula K 2 0.3A1 2 3 .4S03 .6H 2 0.The percentage composition of the pure mineral, according to Dana, 1 is as follows:The mineral usually occurs as a massive, fine-grained, pinkish- white rock breaking with a conchoidal fracture.Some of the coarser varieties are distinctly crystalline in character.While theoretically it should contain over 11 per cent of potash, it is seldom found in minable quantities running over 9.5 or 10 per cent in potash.It is frequently contaminated with quartz and the silicates of potash from which it is derived.The mineral is insoluble in water, but soluble in strong sulphuric aoid.On heating to a moderate tempera- ture (500° C.) water is driven off and the mineral decomposes into alumina and potassium aluminum sulphate.2 Upon increasing the temperature (to 700° to 750° C.) the latter compound is decomposed, fumes of sulphur dioxide and trioxide are evolved, and a residue remains which consists of alumina and soluble potassium sulphate. GEOLOGICAL OCCURRENCE AND ORIGIN.Alunite forms seams in trachytic and similar rocks, being produced by the alteration of such rocks by means of sulphurous vapors or sulphate solutions.It is believed to be closely related in origin to metal veins.Ransome 3 has discussed the various methods by which alunite deposits may be formed, and Butler and Gale 4 quote extensively from the former in their description of a deposit southwest of Marysvale, Utah.The latter authors in discussing the Marysvale alunite state that they consider the main vein in this locality a fissure filling and not a replacement of the wall rock, and cite, as proof of this theory, the fact that the alunite contains but little silica, while in the wall rock where replacement has taken place quartz phenocrysts remain practically unaltered.They conclude that the mineral vein was introduced in part at least by solutions of deep-seated origin.1 System of Mineralogy. 2 As a matter of fact it is very difficult to drive off the water of constitution without also driving off some of the oxides of sulphur.
Source: U.S. Dept. of Agriculture eBooks
Author: William H. Waggaman
Language: English
Subfield: Metals and Alloys
Field: Materials Science
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2478001095