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ALKALI FELDSPAR

Miscellaneous

• Family: Feldspar
• Region: None
• Mined At: Unspecified
• Raw Mineral: Yes
• Generic: No

Notes

(Richard Willis)

Any of several common alumino-silicate minerals that often occur as variously colored glassy crystals regarded as mixtures of sodium aluminosilicate (NaAlSi₃O₈) at one end and of potassium aluminosilicate (KAlSi₃O₈) at the other end of a continuum of class members with varying proportions of Na and K. Both the sodium and potassium aluminosilicates have several distinct forms, each form with a different structure. The forms stable at high temperatures include high-albite (sodium) and sanidine, and high-sanidine (potassium). Low-temperature forms include albite (sodium), and orthoclase and microcline (potassium). The alkali feldspars are important constituents of rocks and are very widespread and abundant in alkali and acidic igneous rocks (particularly syenites, granites, and granodiorites), in pegmatites, and in gneisses.
global categories (see feldspars and minerals)
—— alkali feldspars: a continuum between orthoclase and albite
—— plagioclase feldspars: a continuum between albite and anorthite

Authors

• Richard Willis (Owner)

XML

<?xml version="1.0" encoding="UTF-8"?>
<material name="ALKALI FELDSPAR" descrip="" generic="0" rawmineral="1" searchkey="" loi="0.00">
<families>
<family name="Feldspar"/>
</families>
<notes>
<note>Any of several common alumino-silicate minerals that often occur as variously colored glassy crystals regarded as mixtures of sodium aluminosilicate (NaAlSi&lt;FONT SIZE=2&gt;&lt;SUB&gt;3&lt;/SUB&gt;&lt;/FONT&gt;O&lt;FONT SIZE=2&gt;&lt;SUB&gt;8&lt;/SUB&gt;&lt;/FONT&gt;) at one end and of potassium aluminosilicate (KAlSi&lt;FONT SIZE=2&gt;&lt;SUB&gt;3&lt;/SUB&gt;&lt;/FONT&gt;O&lt;FONT SIZE=2&gt;&lt;SUB&gt;8&lt;/SUB&gt;&lt;/FONT&gt;) at the other end of a continuum of class members with varying proportions of Na and K. Both the sodium and potassium aluminosilicates have several distinct forms, each form
with a different structure. The forms stable at high temperatures include high-albite (sodium) and sanidine, and high-sanidine (potassium). Low-temperature forms include albite (sodium), and orthoclase and microcline (potassium). The alkali feldspars are important constituents of rocks and are very widespread and abundant in alkali and acidic igneous rocks (particularly syenites, granites, and granodiorites), in pegmatites, and in gneisses.&lt;BR&gt;
&lt;B&gt;global categories &lt;/B&gt;(&lt;FONT SIZE=2&gt;see &lt;I&gt;feldspars&lt;/I&gt; and &lt;I&gt;minerals&lt;/I&gt;)&lt;/FONT&gt;&lt;B&gt;&lt;BR&gt;
&amp;#151;&amp;#151; &lt;I&gt;alkali feldspars&lt;/I&gt;&lt;/B&gt;: a continuum between &lt;I&gt;orthoclase&lt;/I&gt; and &lt;I&gt;albite&lt;/I&gt;&lt;BR&gt;
&amp;#151;&amp;#151; &lt;B&gt;&lt;I&gt;plagioclase feldspars:&lt;/I&gt;&lt;/B&gt; a continuum between &lt;I&gt;albite&lt;/I&gt; and &lt;I&gt;anorthite&lt;/I&gt;&lt;BR&gt;

</note>
</notes>
</material>

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