<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:creator>Wiedenmann, Daniel</dc:creator>
  <dc:creator>Zaitsev, A. N.</dc:creator>
  <dc:creator>Britvin, S. N.</dc:creator>
  <dc:creator>Krivovichev, S. V.</dc:creator>
  <dc:creator>Keller, J.</dc:creator>
  <dc:date>2009</dc:date>
  <dc:description xmlns:ns0="xml" ns0:lang="en">Alumoåkermanite, (CaNa)₂(Al,Mg,Fe²⁺)(Si₂O₇), is a new mineral member of the melilite group from the active carbonatite-nephelinite-phonolite volcano Oldoinyo Lengai, Tanzania. The mineral occurs as tabular phenocrysts and microphenocrysts in melilite-nephelinitic ashes and lapilli-tuffs. Alumoåkermanite is light brown in colour; it is transparent, with a vitreous lustre and the streak is white. Cleavages or partings are not observed. The mineral is brittle with an uneven fracture. The measured density is 2.96(2) g/cm³. The Mohs hardness is ∼4.5-6. Alumoåkermanite is uniaxial (-) with ω = 1.635(1) and ε = 1.624-1.626(1). In a 30 μm thin section (+N), the mineral has a yellow to orange interference colour, straight extinction and positive elongation, and is nonpleochroic. The average chemical formula of the mineral derived from electron microprobe analyses is: (Ca&lt;sub&gt;1.48&lt;/sub&gt;Na&lt;sub&gt;0.50&lt;/sub&gt;Sr&lt;sub&gt;0.02&lt;/sub&gt;K&lt;sub&gt;0.01&lt;/sub&gt;)&lt;sub&gt;Σ2.01&lt;/sub&gt;(Al&lt;sub&gt;0.44&lt;/sub&gt;Mg&lt;sub&gt;0.30&lt;/sub&gt;Fe²⁺&lt;sub&gt;0.17&lt;/sub&gt;Fe³⁺&lt;sub&gt;0.07&lt;/sub&gt;Mn&lt;sub&gt;0.01&lt;/sub&gt;)&lt;sub&gt;Σ0.99&lt;/sub&gt;(Si&lt;sub&gt;1.99&lt;/sub&gt;Al&lt;sub&gt;0.01&lt;/sub&gt;O₇). Alumoåkermanite is tetragonal, space group &lt;i&gt;P&lt;/i&gt;42₁&lt;i&gt;m&lt;/i&gt; with &lt;i&gt;a&lt;/i&gt; = 7.7661(4) Å, &lt;i&gt;c&lt;/i&gt; = 5.0297(4) Å, &lt;i&gt;V&lt;/i&gt; = 303.4(1) Å³ and &lt;i&gt;Z&lt;/i&gt; = 2. The five strongest powder-diffraction lines [&lt;i&gt;d&lt;/i&gt; in Å, (&lt;i&gt;I&lt;/i&gt;/&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;o&lt;/sub&gt;), &lt;i&gt;hkl&lt;/i&gt;] are: 3.712, (13), (111); 3.075, (25), (201); 2.859, (100), (211); 2.456, (32), (311); 1.757, (19), (312). Single-crystal structure refinement (&lt;i&gt;R&lt;/i&gt;₁ = 0.018) revealed structure topology typical of the melilite-group minerals, i.e. tetrahedral [(Al,Mg)(Si₂O₇)] sheets interleaved with layers of (CaNa) cations. The name reflects the chemical composition of the mineral.</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>https://folia.unifr.ch/global/documents/301248</dc:identifier>
  <dc:identifier>https://folia.unifr.ch/documents/301248/files/wiedenmann_anm.pdf</dc:identifier>
  <dc:language>eng</dc:language>
  <dc:relation>info:eu-repo/semantics/altIdentifier/doi/10.1180/minmag.2009.073.3.373</dc:relation>
  <dc:rights>info:eu-repo/semantics/openAccess</dc:rights>
  <dc:rights>License undefined</dc:rights>
  <dc:source>Mineralogical Magazine. - 2009, vol. 73, no. 3, p. 373-384</dc:source>
  <dc:subject xmlns:ns1="xml" ns1:lang="en">Alumoåkermanite</dc:subject>
  <dc:subject xmlns:ns2="xml" ns2:lang="en">Åkermanite</dc:subject>
  <dc:subject xmlns:ns3="xml" ns3:lang="en">melilite</dc:subject>
  <dc:subject xmlns:ns4="xml" ns4:lang="en">new mineral</dc:subject>
  <dc:subject xmlns:ns5="xml" ns5:lang="en">volcanic rock</dc:subject>
  <dc:subject xmlns:ns6="xml" ns6:lang="en">chemical composition</dc:subject>
  <dc:subject xmlns:ns7="xml" ns7:lang="en">crystal structure</dc:subject>
  <dc:subject xmlns:ns8="xml" ns8:lang="en">Oldoinyo lengai</dc:subject>
  <dc:subject xmlns:ns9="xml" ns9:lang="en">Tanzania</dc:subject>
  <dc:subject>info:eu-repo/classification/udc/549</dc:subject>
  <dc:title xmlns:ns10="xml" ns10:lang="en">Alumoåkermanite, (Ca,Na)₂(Al,Mg,Fe²⁺)(Si₂O₇), a new mineral from the active carbonatite-nephelinite-phonolite volcano Oldoinyo Lengai, northern Tanzania</dc:title>
  <dc:type>http://purl.org/coar/resource_type/c_6501</dc:type>
</oai_dc:dc>