<?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>A.H. Truesdell</dc:contributor>
  <dc:contributor>Richard C. Erd</dc:contributor>
  <dc:creator>C. L. Christ</dc:creator>
  <dc:date>1967</dc:date>
  <dc:description>&lt;p&gt;The significant known hydrated borate mineral assemblages (principally of the western United States) in the system Na&lt;sub&gt;2&lt;/sub&gt;O-CaO-MgO-B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3-&lt;/sub&gt;H&lt;sub&gt;2&lt;/sub&gt;O are expressible in three ternary composition diagrams. Phase rule interpretation of the diagrams is consistent with observation, if the activity of H&lt;sub&gt;2&lt;/sub&gt;O is generally considered to be determined by the geologic environment. The absence of conflicting tie-lines on a diagram indicates that the several mineral assemblages of the diagram were formed under relatively narrow ranges of temperature and pressure.&lt;/p&gt;&lt;p&gt;The known structural as well as empirical formulas for the minerals are listed, and the more recent (since 1960) crystal structure findings are discussed briefly.&lt;/p&gt;&lt;p&gt;Schematic Gibbs free energy-composition diagrams based on known solubility-temperature relations in the systems Na&lt;sub&gt;2&lt;/sub&gt;B&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;-H&lt;sub&gt;2&lt;/sub&gt;O and Na&lt;sub&gt;2&lt;/sub&gt;B&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;-NaCl-H&lt;sub&gt;2&lt;/sub&gt;O, are highly useful in the interpretation and prediction of the stability relations in these systems; in particular these diagrams indicate clearly that tincalconite, although geologically important, is everywhere a metastable phase. Crystal-chemical considerations indicate that the same thermodynamic and kinetic behavior observed in the Na&lt;sub&gt;2&lt;/sub&gt;B&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;-H&lt;sub&gt;2&lt;/sub&gt;O system will hold in the Ca&lt;sub&gt;2&lt;/sub&gt;B&lt;sub&gt;6&lt;/sub&gt;O&lt;sub&gt;11&lt;/sub&gt;-H&lt;sub&gt;2&lt;/sub&gt;O system. This conclusion is confirmed by the petrologic evidence.&lt;/p&gt;&lt;p&gt;The chemical relations among the mineral assemblages of a ternary diagram are expressed by a schematic “activity-activity” diagram. These activity-activity diagrams permit the tracing-out of the paragenetic sequences as a function of changing cation and H&lt;sub&gt;2&lt;/sub&gt;O activities.&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1016/0016-7037(67)90045-2</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Elsevier</dc:publisher>
  <dc:title>Borate mineral assemblages in the system Na2O-CaO-MgO-B2O3-H2O</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>