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<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>D. R. Wones</dc:contributor>
  <dc:creator>H.P. Eugster</dc:creator>
  <dc:date>1962</dc:date>
  <dc:description>&lt;p&gt;&lt;span class="ScopusTermHighlight"&gt;Annite&lt;/span&gt;&lt;span&gt;, KFe&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;AISi&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;O&lt;/span&gt;&lt;sub&gt;10&lt;/sub&gt;&lt;span&gt;(OH)&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;a member of the iron biotites and the ferrous analogue of phlogopite, has been synthesized and its phase&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;relations&lt;/span&gt;&lt;span&gt;&amp;nbsp;have been determined as functions of temperature, fugacity of oxygen (fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;), and total pressure (P&lt;/span&gt;&lt;sub&gt;total&lt;/sub&gt;&lt;span&gt;≈PH&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;O+PH&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;). A method for controlling fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;at high total pressures is described, and data for the 'oxygen buffers' used are given. Buffers range from quartz+iron+fayalite assemblages (low fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;) to magnetite-hematite assemblages (high fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;). Optical properties and unit-cell dimensions of synthetic annites depend on the conditions of synthesis.By recalculating published analyses of natural iron-rich biotites it can be shown that one cannot assume a constant hydrogen content for such biotites. Oxidation may have occurred by drying at 115°C. Octahedral occupancy therefore cannot be calculated from such data.Phase&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;relations&lt;/span&gt;&lt;span&gt;&amp;nbsp;of&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;annite&lt;/span&gt;&lt;span&gt;&amp;nbsp;are presented in 2,070 and 1,035 bar sections. Depending on fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;-T values&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;annite&lt;/span&gt;&lt;span&gt;&amp;nbsp;was found to decompose to one of the following assemblages: hematite+ sanidine, magnetite+sanidine, fayalite+leucite+kalsilite, iron+sanidine. All decompositions are dehydration and redox reactions and are sensitive to changes in fH&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;0 and fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;(or fH&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;0 and fH&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;). At 2, 070 bars total pressure&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;annite&lt;/span&gt;&lt;span&gt;+magnetite+sanidine can coexist between 425°C and 825° C, depending upon the magnitude of fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;.In the presence of quartz the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;stability&lt;/span&gt;&lt;span&gt;&amp;nbsp;field of&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;annite&lt;/span&gt;&lt;span&gt;&amp;nbsp;is more restricted. Phase equilibria in the system KAlSiO&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;-SiO&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;-Fe-O&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;-H&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;have been summarized schematically.Wherever possible, thermodynamic extrapolations are made to test the internal consistency of the data. Enthalpies of formation are calculated for both&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;annite&lt;/span&gt;&lt;span&gt;&amp;nbsp;and phlogopite. Ranges of fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;values in nature as well as mechanisms for changes in fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;are investigated. It is useful to distinguish between assemblages which are internally buffered with respect to fo&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;changes and those which are not buffered. The applications of individual reactions involving&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;annite&lt;/span&gt;&lt;span&gt;&amp;nbsp;to specific geologic problems are discussed with respect to igneous, metamorphic, and sedimentary rocks.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1093/petrology/3.1.82</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Oxford University Press</dc:publisher>
  <dc:title>Stability relations of the ferruginous biotite, annite</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>