The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

(80 ECONOMIC GEOLOGY The strength of this * argillaceous sandstone" had been over-estimated four-fold, despite the warning of the French geologists, Bertrand and O. Zurcher, who had found in pre- paring thin sections that water reduced it to mud. VARIETIES OF BuiLpiNg Stones—The most durable of building stones is granite, which in the stone trade includes all coarse-grained igneous rocks such as syenite, diorite, and gabbro, and sometimes even granular marble. Granite, as defined in geology, consists of quartz, white mica, and ortho- clase felspar, and owes its durability to their chemical stability. Its absorption of water is very low and often less than 1 per cent. The chief trouble with granite is * spalling or development of cracks parallel to the surface owing to the three constituents expanding unequally on change of tem- perature. The basic plutonic rocks decay by weathering more readily than granite, and being heavier are more expensive to handle. The extra weight is an advantage for some uses, as in break- waters. Limestones are favourite building stones owing to their lightness, beauty, and ease of working. They are as a rule unsuitable for use in cities, as they decay in an acid atmo- sphere. The carbonate of lime on the surface may be con- verted into a fur of sulphate, which is easily removed and leaves another layer liable to the same change. Dolomite, being less soluble than carbonate of lime, may be more durable; but the Houses of Parliament at Westminster show that poor dolomite decays rapidly. The stone re- commended for that building was used at the same date for the Geological Survey Museum, three-quarters of a mile distant, and it has lasted exceptionally well. In the Houses of Parliament, owing to the difficulty of getting an adequate supply, dolomite of very inferior quality was accepted. A subsequent Royal Commission reported that much of it ought not to have been used for building under anv conditions whatever. Sandstone is largely used in cities being less expensive than granite and more durable than limestone. The dura- bility of sandstone depends mainly upon its cement. The best sandstones consist of quartz grains in a siliceous cement, Iron oxide cements, which colour stones red or brown, are generally stable.

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