<?xml version='1.0' encoding='utf-8'?>
<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>J.E. Taggart Jr.</dc:contributor>
  <dc:creator>E.E. Foord</dc:creator>
  <dc:date>1998</dc:date>
  <dc:description>&lt;p&gt; &lt;span&gt;The turquoise group has the general formula: A (sub 0-1) B&amp;nbsp;&lt;/span&gt;&lt;sub&gt;6&lt;/sub&gt;&lt;span&gt;&amp;nbsp;(PO&amp;nbsp;&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;&amp;nbsp;) (sub 4-x) (PO&amp;nbsp;&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;OH)&amp;nbsp;&lt;/span&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;span&gt;&amp;nbsp;(OH)&amp;nbsp;&lt;/span&gt;&lt;sub&gt;8&lt;/sub&gt;&lt;span&gt;&amp;nbsp;.4H&amp;nbsp;&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;O, where x = 0-2, and consists of six members: planerite, turquoise, faustite, aheylite, chalcosiderite and an unnamed Fe (super 2+) -Fe (super 3+) analogue. The existence of "coeruleolactite" is doubtful. Planerite is revalidated as a species and is characterized by a dominant A-site vacancy. Aheylite is established as a new member of the group, and is characterized by having Fe (super 2+) dominant in the A-site. Chemical analyses of 15 pure samples of microcrystalline planerite, turquoise, and aheylite show that a maximum of two of the (PO&amp;nbsp;&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;&amp;nbsp;) groups are protonated (PO&amp;nbsp;&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;OH) in planerite. Complete solid solution exists between planerite and turquoise. Other members of the group show variable A-site vacancy as well. Most samples of "turquoise" are cation-deficient or are planerite. Direct determination of water indicates that there are 4 molecules of water. Planerite, ideally []Al&amp;nbsp;&lt;/span&gt;&lt;sub&gt;6&lt;/sub&gt;&lt;span&gt;&amp;nbsp;(PO&amp;nbsp;&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;&amp;nbsp;)&amp;nbsp;&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;(PO&amp;nbsp;&lt;/span&gt;&lt;sub&gt;3&lt;/sub&gt;&lt;span&gt;&amp;nbsp;OH)&amp;nbsp;&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;(OH)&amp;nbsp;&lt;/span&gt;&lt;sub&gt;8&lt;/sub&gt;&lt;span&gt;&amp;nbsp;.4H&amp;nbsp;&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;O, is white, pale blue or pale green, and occurs as mamillary, botryoidal crusts as much as several mm thick; may also be massive; microcrystalline, crystals typically 2-4 micrometres, luster chalky to earthy, H. 5, somewhat brittle, no cleavage observed, splintery fracture, D&amp;nbsp;&lt;/span&gt;&lt;sub&gt;m&lt;/sub&gt;&lt;span&gt;&amp;nbsp;2.68(2), D&amp;nbsp;&lt;/span&gt;&lt;sub&gt;c&lt;/sub&gt;&lt;span&gt;&amp;nbsp;2.71, not magnetic, not fluorescent, mean RI about 1.60. a 7.505(2), b 9.723(3), c 7.814(2) Aa, alpha 111.43 degrees , beta 115.56 degrees , Gamma 68.69 degrees , V 464.2(1) Aa&amp;nbsp;&lt;/span&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;&amp;nbsp;, Z = 1. Aheylite, ideally Fe (super 2+) Al&amp;nbsp;&lt;/span&gt;&lt;sub&gt;6&lt;/sub&gt;&lt;span&gt;&amp;nbsp;(PO&amp;nbsp;&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;&amp;nbsp;)&amp;nbsp;&lt;/span&gt;&lt;sub&gt;4&lt;/sub&gt;&lt;span&gt;&amp;nbsp;(OH)&amp;nbsp;&lt;/span&gt;&lt;sub&gt;8&lt;/sub&gt;&lt;span&gt;&amp;nbsp;.4H&amp;nbsp;&lt;/span&gt;&lt;sub&gt;2&lt;/sub&gt;&lt;span&gt;&amp;nbsp;O, is pale blue or green, and occurs as isolated and aggregate clumps of hemispherical or spherical, radiating to interlocked masses of crystals that average 3 micrometres in maximum dimension; porcelaneous-subvitreous luster, moderate to brittle tenacity, no cleavage observed, hackly to splintery fracture, not magnetic, not fluorescent, biax. (+), mean RI is about 1.63, D&amp;nbsp;&lt;/span&gt;&lt;sub&gt;m&lt;/sub&gt;&lt;span&gt;&amp;nbsp;2.84(2), D&amp;nbsp;&lt;/span&gt;&lt;sub&gt;c&lt;/sub&gt;&lt;span&gt;&amp;nbsp;2.90. a 7.400(1), b 9.896(1), c 7.627(1) Aa, alpha 110.87 degrees , beta 115.00 degrees , gamma 69.96 degrees , V 460.62(9) Aa&amp;nbsp;&lt;/span&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;&amp;nbsp;, Z = 1.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1180/002646198547495</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Cambridge University Press</dc:publisher>
  <dc:title>A reexamination of the turquoise group: The mineral aheylite, planerite (redefined), turquoise and coeruleolactite</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>