This work presents a study of an unusual synthetic diamond sample, where calcite is the main phase in addition to diamond. Using Raman spectroscopy it can be shown that in addition to diamond carbon forms four different generations: highly ordered graphite-II, lower ordered graphite-I as spandrel between different mineral grains, weakly-ordered carbonaceous material as graphite-III and the hexagonal diamond lonsdaleite (here graphite-IV) as last formation in calcite. Graphite-III can be found mainly in the calcite body. According to the fine dispersion of this carbonaceous material and the arrangement on grain boundaries, we assume that carbon was dissolved in the calcite melt, and that by the activated state of carbon in the calcite melt the formation of diamond is favored near 1760°C, and 6.8 GPa. Lonsdaleite as minor phase may have been formed as an longlived intermediate state under standard conditions between graphite and diamond. Evidence shows that there are two different lonsdaleite phases (possibly hexagonal and monocline) present. The prevailing diamond is characterized by the first-order Raman line at 1333 cm^-1. However, there are also present diamonds with the first-order Raman line down to 1310.6 cm-1, corresponding to ¹³C = 0.511. Significantly there is the strong decrease of the optical damage threshold with increase of the ¹³C content.

Item Type:	Refereed Article
Keywords:	diamond, 13C-rich diamond, calcite, graphite, lonsdaleite, Raman spectroscopy
Research Division:	Chemical Sciences
Research Group:	Inorganic chemistry
Research Field:	Non-metal chemistry
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the chemical sciences
UTAS Author:	Davidson, P (Dr Paul Davidson)
ID Code:	148605
Year Published:	2021
Deposited By:	CODES ARC
Deposited On:	2022-01-27
Last Modified:	2022-04-20
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