Abstract
Stability relations of Co 2SiO 4 have been studied over the temperature range 715° to 1530 °C in the pressure range 59 to 93 kb with the aid of a tetrahedral anvil type of high-pressure apparatus. It was found that at temperatures below about 930 °C the olivine polymorph of Co 2SiO 4 (Co 2SiO 4 I) transformed directly to the spinel polymorph (Co 2SiO 4 III) at high pressures. At the higher temperatures, however, a new high-pressure polymorph with orthorhombic structure (Co 2SiO 4 II) was observed in the pressure range intermediate between the olivine and the spinel field. The triple point in the system Co 2SiO 4 I (olivine) Co 2SiO 4 II Co 2SiO 4 III (spinel) was approximately determined to be at 930 °C and 68 kb. Density increases associated with the Co 2SiO 4 I Co 2SiO 4 II transformation and the Co 2SiO 4 II Co 2SiO 4 III transformation were estimated to be 7.1% and 2.5%. It is suggested that the analogous stepwise phase transformation from olivine to spinel through an intermediate orthorhombic phase might be excepted in the mantle olivine.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
