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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>Howard T. Evans Jr.</dc:contributor>
  <dc:contributor>Gordon L. Nord Jr.</dc:contributor>
  <dc:contributor>Edward J. Dwornik</dc:contributor>
  <dc:contributor>Charles Milton</dc:contributor>
  <dc:creator>Daniel E. Appleman</dc:creator>
  <dc:date>1987</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;Delindeite and lourenswalsite are two new barium titanosilicate minerals found as microscopic crystals in miarolitic cavities in nepheline syenite in the Diamond Jo quarry, Hot Spring County, Arkansas. Delindeite is found as aggregates of flake-like crystallites in compact spherules, light pinkish grey in colour, with a resinous, pearly lustre. The flakes are biaxial positive with average&amp;nbsp;&lt;/span&gt;&lt;i&gt;&lt;span class="italic"&gt;n&lt;/span&gt;&lt;/i&gt;&lt;span&gt;&amp;nbsp;∼ 1.813; the measured density is 3.3 g/cm&lt;/span&gt;&lt;sup&gt;&lt;span class="sup"&gt;3&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;. Electron diffraction revealed a monoclinic unit cell in space group&amp;nbsp;&lt;/span&gt;&lt;span class="italic"&gt;C&lt;/span&gt;&lt;span&gt;2&lt;i&gt;l&lt;/i&gt;&lt;/span&gt;&lt;i&gt;&lt;span class="italic"&gt;m&lt;/span&gt;&lt;/i&gt;&lt;span&gt;&amp;nbsp;or subgroup, with&amp;nbsp;&lt;/span&gt;&lt;i&gt;&lt;span class="italic"&gt;a&lt;/span&gt;&lt;/i&gt;&lt;span&gt;&amp;nbsp;= 21.617(13),&amp;nbsp;&lt;/span&gt;&lt;i&gt;&lt;span class="italic"&gt;b&lt;/span&gt;&lt;/i&gt;&lt;span&gt;&amp;nbsp;= 6.816(5),&amp;nbsp;&lt;/span&gt;&lt;i&gt;&lt;span class="italic"&gt;c&lt;/span&gt;&lt;/i&gt;&lt;span&gt;&amp;nbsp;= 5.383(3) Å,&amp;nbsp;&lt;/span&gt;&lt;span class="italic"&gt;β&lt;/span&gt;&lt;span&gt;&amp;nbsp;= 94.03(5)° (refined from X-ray powder data). The strongest X-ray lines are (&lt;/span&gt;&lt;span class="italic"&gt;&lt;i&gt;hkl&lt;/i&gt;, &lt;i&gt;d&lt;/i&gt;&lt;/span&gt;&lt;sub&gt;&lt;span class="sub"&gt;obs&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;,&amp;nbsp;&lt;/span&gt;&lt;i&gt;&lt;span class="italic"&gt;I&lt;/span&gt;&lt;/i&gt;&lt;sub&gt;&lt;span class="sub"&gt;rel&lt;/span&gt;&lt;/sub&gt;): (200, 10.80, 100); (311, 3.54, 24); (6̄01, 3.083, 28); (601, 2.888, 31); (2̄21, 2.806, 20); (910, 2.262,18). The crystals are submicroscopically twinned on (100) and also produce additional continuous diffraction streaks parallel to&amp;nbsp;&lt;span class="italic"&gt;a&lt;/span&gt;*, which double the&amp;nbsp;&lt;span class="italic"&gt;b&lt;/span&gt;&amp;nbsp;and&amp;nbsp;&lt;span class="italic"&gt;c&lt;/span&gt;&amp;nbsp;axes. The formula derived from electron and ion probe analyses (H&lt;sub&gt;&lt;span class="sub"&gt;2&lt;/span&gt;&lt;/sub&gt;O by difference), as constrained by density and molar volume data, is approximately (Na,K)&lt;sub&gt;&lt;span class="sub"&gt;2.7&lt;/span&gt;&lt;/sub&gt;(Ba,Ca)&lt;sub&gt;&lt;span class="sub"&gt;4&lt;/span&gt;&lt;/sub&gt;(Ti,Fe,Al)&lt;sub&gt;&lt;span class="sub"&gt;6&lt;/span&gt;&lt;/sub&gt;Si&lt;sub&gt;&lt;span class="sub"&gt;8&lt;/span&gt;&lt;/sub&gt;O&lt;sub&gt;&lt;span class="sub"&gt;26&lt;/span&gt;&lt;/sub&gt;(OH)&lt;sub&gt;&lt;span class="sub"&gt;14&lt;/span&gt;&lt;/sub&gt;, with Na &amp;gt; K, Ba ≫ Ca, Ti ≫ Fe,Al;&amp;nbsp;&lt;i&gt;&lt;span class="italic"&gt;Z&lt;/span&gt;&amp;nbsp;&lt;/i&gt;= 1. Lourenswalsite occurs as very thin hexagonal plates in rosettes, silver grey to light brownish grey in colour. The crystals are biaxial negative with very low 2&lt;i&gt;&lt;span class="italic"&gt;V&lt;/span&gt;&lt;/i&gt;&amp;nbsp;angle. Indices of refraction are&amp;nbsp;&lt;span class="italic"&gt;n&lt;sub&gt;&lt;i&gt;&lt;span class="sub"&gt;α&lt;/span&gt;&lt;/i&gt;&lt;/sub&gt;&lt;/span&gt;&amp;nbsp;= 1.815,&amp;nbsp;&lt;span class="italic"&gt;&lt;i&gt;n&lt;sub&gt;&lt;span class="sub"&gt;β&lt;/span&gt;&lt;/sub&gt;&lt;/i&gt;&amp;nbsp;≈ &lt;i&gt;n&lt;sub&gt;&lt;span class="sub"&gt;γ&lt;/span&gt;&lt;/sub&gt;&lt;/i&gt;&lt;/span&gt;&amp;nbsp;= 1.840; the measured density is 3.17 g/cm = 1.840; the measured density is 3.17 g/cm&lt;sup&gt;&lt;span class="sup"&gt;3&lt;/span&gt;&lt;/sup&gt;. X-ray and electron diffraction show a sharp pseudohexagonal lattice with&amp;nbsp;&lt;span class="italic"&gt;a&lt;/span&gt;&amp;nbsp;= 5.244 Å, but extremely diffuse diffraction streaks normal to the&amp;nbsp;&lt;i&gt;&lt;span class="italic"&gt;hk&lt;/span&gt;&lt;/i&gt;0 plane. In these streaks a period of 20.5 Å can be discerned. A hexagonal unit cell with&amp;nbsp;&lt;i&gt;&lt;span class="italic"&gt;a&lt;/span&gt;&lt;/i&gt;&amp;nbsp;= 5.244(2) Å,&amp;nbsp;&lt;i&gt;&lt;span class="italic"&gt;c&lt;/span&gt;&lt;/i&gt;&amp;nbsp;= 20.49(3) Å can be refined from the powder diffraction data but does not account for some lines, probably because of extreme layer disorder as shown by precession single-crystal patterns. The strong X-ray powder lines are (002, 10.22, 20); (-, 3.93, 20); (111, 2.608, 100); (300, 1.5145, 80); (220, 1.3111, 25). The formula given by microprobe analyses, constrained by density and molar volume data, is approximately (K,Ba)&lt;sub&gt;&lt;span class="sub"&gt;2&lt;/span&gt;&lt;/sub&gt;(Ti,Mg,Ca,Fe)&lt;sub&gt;&lt;span class="sub"&gt;4&lt;/span&gt;&lt;/sub&gt;(Si,Al,Fe)&lt;sub&gt;&lt;span class="sub"&gt;6&lt;/span&gt;&lt;/sub&gt;O&lt;sub&gt;&lt;span class="sub"&gt;14&lt;/span&gt;&lt;/sub&gt;(OH)&lt;sub&gt;&lt;span class="sub"&gt;12&lt;/span&gt;&amp;nbsp;&lt;/sub&gt;with K &amp;gt; Ba, Ti ≫ (Mg,Ca,Fe), Si &amp;gt; Al &amp;gt; Fe;&amp;nbsp;&lt;span class="italic"&gt;Z&lt;/span&gt;&amp;nbsp;= 1. These minerals are formed under oxidizing weathering conditions, and iron is assumed to be in the Fe&lt;sup&gt;&lt;span class="sup"&gt;3+&lt;/span&gt;&lt;/sup&gt;&amp;nbsp;state.&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1180/minmag.1987.051.361.08</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Cambridge University Press</dc:publisher>
  <dc:title>Delindeite titanosilicates and lourenswalsite, two new from the Magnet Cove region, Arkansas</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>