• WordNet 3.6
    • n feldspar any of a group of hard crystalline minerals that consist of aluminum silicates of potassium or sodium or calcium or barium
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Webster's Revised Unabridged Dictionary
    • n Feldspar (Min) A name given to a group of minerals, closely related in crystalline form, and all silicates of alumina with either potash, soda, lime, or, in one case, baryta. They occur in crystals and crystalline masses, vitreous in luster, and breaking rather easily in two directions at right angles to each other, or nearly so. The colors are usually white or nearly white, flesh-red, bluish, or greenish.☞ The group includes the monoclinic (orthoclastic) species orthoclase or common potash feldspar, and the rare hyalophane or baryta feldspar; also the triclinic species (called in general plagioclase microcline, like orthoclase a potash feldspar; anorthite or lime feldspar; albite or soda feldspar; also intermediate between the last two species, labradorite andesine oligoclase, containing both lime and soda in varying amounts. The feldspars are essential constituents of nearly all crystalline rocks, as granite, gneiss, mica, slate, most kinds of basalt and trachyte, etc. The decomposition of feldspar has yielded a large part of the clay of the soil, also the mineral kaolin, an essential material in the making of fine pottery. Common feldspar is itself largely used for the same purpose.
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Century Dictionary and Cyclopedia
    • n feldspar In mineralogy, one of a very common group of closely related minerals, all silicates of aluminium, together with either calcium, sodium, potassium, or in one case barium. They crystallize in the monoclinic or triclinic system with closely similar angles. The prismatic angle is not far from 120°, and they have two easy cleavages which make an angle of 90°, or nearly 90°, with each other. Their specific gravity lies between 2.6 and 2.8, and their hardness between 6 and 7. In color they vary from clear and glassy to white, grayish, and light shades of yellow, red, or green, rarely darker green to black. They occur in distinct crystals, also in massive forms varying in structure from coarsely cleavable to granular-crystalline, compact, and hornstone-like. They form an essential constituent of many of the common crystalline rocks, as granite, gneiss, syenite, diorite, most kinds of basalt, andesite, trachyte, etc. The monoclinic feldspars are orthoclase and hyalophane. The former is a potash feldspar (see orthoclase), and is the commonest of the group; the latter is a baryta feldspar, and is a rare species. Closely related to orthoclase is the triclinic microcline (which see), having the same composition, but varying slightly in form. Besides these there are the triclinic (lime-soda) feldspars, called in general plagioclase, because of the oblique angle between their two cleavages, and forming a series varying progressively in composition, form, optical characters, and specific gravity from the lime feldspar anorthite to the sodium feldspar albite; the intermediate species are considered as isomorphous compounds of these two extremes in varying proportions. Those ordinarily recognized are, named in order, labradorite, andesin, and oligoclase, the last approaching most closely to albite. The increase in soda in the members of the series is accompanied by an increase of silica, the species being increasingly acidic in the order named: thus, anorthite contains 43 per cent, of silica, and albite 69 per cent. The specific gravity diminishes in the series from anorthite (2.75) to albite (2.61). Certain triclinic feldspars containing considerable potash and with an angle of cleavage varying but little from 90° are sometimes grouped under the name anorthoclase. Common feldspar, or orthoclase (and microcline), is much used in the manufacture of porcelain; some kinds are employed for ornaments, as aventurin feldspar or sunstone, also moonstone (an opalescent variety of orthoclase), albite or oligoclase, and, most of all, the species labradorite, beautiful for its play of colors Also felspar.
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Chambers's Twentieth Century Dictionary
    • n Feldspar feld′spär (min.) a general term for the most important rock-forming group of minerals—all anhydrous silicates of alumina—divided into those in which the minerals crystallise in monoclinic and in triclinic forms—also Fel′spar, Feld′spath
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Webster's Revised Unabridged Dictionary
G. feldspath,; feld, field + spath, spar
Chambers's Twentieth Century Dictionary
Ger. feldspathfeld, a field, spath, spar.


In literature:

Composed of Quartz, Feldspar, and Mica.
"Two Expeditions into the Interior of Southern Australia, Volume I" by Charles Sturt
Thus he formed, for instance, pumice-stone, feldspar, mica, iron pyrites, &c. artificially.
"Familiar Letters of Chemistry" by Justus Liebig
Sienite and feldspar succeeded in our descent to the snow line, where we found a feldspathic granite.
"The Life and Adventures of Kit Carson, the Nestor of the Rocky Mountains, from Facts Narrated by Himself" by De Witt C. Peters
Feldspar, rock grains called, 63.
"Conservation Reader" by Harold W. Fairbanks
It is estimated that the feldspars make up 50 per cent of all the igneous rocks and 16 per cent of the sedimentary rocks.
"The Economic Aspect of Geology" by C. K. Leith
Similarly opal, moonstone, and turquoise are of about the same hardness as feldspar and are all rated 6.
"A Text-Book of Precious Stones for Jewelers and the Gem-Loving Public" by Frank Bertram Wade
When flint and feldspar are used, they are ground fine at the quarry.
"Makers of Many Things" by Eva March Tappan
If sienite, very hard, the quartz element predominating, as the feldspar does farther north.
"The Atlantic Monthly, Volume 15, No. 91, May, 1865" by Various
What does feldspar rock yield?
"The Elements of Agriculture" by George E. Waring
Granite is made of quartz, feldspar, and mica, sometimes with added particles of hornblende.
"Earth and Sky Every Child Should Know" by Julia Ellen Rogers

In poetry:

And gardens, where, in the myrrh-sweet June,
Magnolias blossom with many a moon
Of fragrance; and, in the feldspar light
Of August, roses bloom red and white.
"The Road Home" by Madison Julius Cawein

In news:

Imerys has signed a final agreement regarding its acquisition of The Feldspar Corp. A subsidiary of Zemex Corp. That includes its feldspar and kaolin activities.
In 2007, The Feldspar Corp.
Has introduced a potash crystalline feldspar mineral compound that is transparent to ultraviolet light.
Sunstone , the plagioclase feldspar mineral has attractive inclusions like hematite that lend a sparkly effect to the cut gemstones.
Obtained by the Chemistry and Mineralogy (CheMin) experiment on NASA's Curiosity rover, these data reveal crystalline feldspar, pyroxenes and olivine mixed with some amorphous (non-crystalline) material.

In science:

Polymerization on internal, organophilic silica surfaces of dealuminated zeolites and feldspars.
Field-control, phase-transitions, and life's emergence
These species should be depleted into feldspars in the presence of silicates; their presence requires the sequestration of condensates to deeper levels1 (Burrows et al. 2000).
Cloud Formation and Dynamics in Cool Dwarf and Hot Exoplanetary Atmospheres