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Log out of Readcube. Click on an option below to access. Log out of ReadCube. The data are of sufficient accuracy to allow detailed examination of structural topology and intracrystalline equilibria and to provide some insight into exsolution phenomena, chemical bonding, and phase transitions. This paper summarizes the results of recent research on olivines, humites, garnets, aluminosilicates, pyroxenes, pyroxenoids, amphiboles, micas, silica minerals, feldspars, feldspathoids, and scapolites.
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Structures, Properties and Occurrences
You previously purchased this article through ReadCube. Institutional Login. Log in to Wiley Online Library. Purchase Instant Access. The feldspathoids are relatively rare.
As noted previously, they are considered here primarily because they are the specific minerals used in naming alkalic igneous rocks. In this role, the feldspathoids, along with minerals of the melilite group, are referred to as foids in the IUGS classification of igneous rocks. Feldspathoids may occur along with feldspars in igneous rocks.
They do not occur in igneous rocks containing original free silica— i. They are, in fact, incompatible with consanguineous quartz that derived from the same parent magma , as is quite apparent from the following equations:. As can be seen from these equations, a feldspar would form in lieu of its feldspathoid chemical analogue in any silica-saturated magma. Nepheline is the most common feldspathoid; it is a major constituent of many alkalic igneous rocks such as nepheline syenites.
Feldspathoids also occur in a few other kinds of rocks— e.
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Nepheline is sometimes used as a source of soda, silica, and alumina in the manufacture of glass and ceramics. Leucite was formerly used in Italy for fertilizer. Sodalite, once treasured as the basic ingredient of ultramarine pigment, is still used as a gemstone and as the desired constituent of many of the blue rocks used as facing stones.
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View Feldspars And Feldspathoids Structures Properties And Occurrences
Table Of Contents. Submit Feedback. Thank you for your feedback. Introduction Chemical composition and crystal structure Physical properties Origin and occurrence Uses. Written By: R.
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See Article History. Chemical composition and crystal structure The feldspathoid group minerals are sodium , potassium, and calcium aluminosilicates, many of which resemble the feldspars in appearance. Physical properties The physical properties of the various feldspathoids differ from those of the feldspars and from one another. Start Your Free Trial Today.
Learn More in these related Britannica articles:. Feldspar , any of a group of aluminosilicate minerals that contain calcium, sodium, or potassium. Of the more than 3, known mineral species, less than 0. Sodium Na , chemical element of the alkali metal group Group 1 [Ia] of the periodic table. Sodium is a very soft silvery-white metal.
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