• journal_title：American Mineralogist
• Contributor：Anat Shahar ; William A. Bassett ; Ho-kwang Mao ; I-Ming Chou ; Wendy Mao
• Publisher：Mineralogical Society of America
• Date：2005-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2005.1783
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：90
• issue：11-12
• firstpage：1835
• section：Articles

Raman analyses of single crystals of ikaite, CaCO₃·6H₂O, synthesized in a diamond-anvil cell at ambient temperature yield spectra from 0.14 to 4.08 GPa; the most intense peaks are at 228 and 1081 cm⁻¹ corresponding to E_g (external) and A_1g (internal) modes of vibrations in CO²⁻ ₃ ions, respectively. These are in good agreement with Raman spectra previously published for ikaite in powder form at ambient temperature and pressure. Visual observations of a sample consisting initially of a mixture of calcite + water in a hydrothermal diamond-anvil cell yielded a P-T phase diagram up to 2 GPa and 120 °C; the boundary for the reaction ikaite ↔ aragonite + water has a positive slope and is curved convexly toward the aragonite + water field similar to typical melt curves. This curvature can be explained in terms of the Clapeyron equation for a boundary between a solid phase and a more compressible liquid phase or largely liquid phase assemblage.