Diamonds have an incredibly high melting point, around 3573°F (1967°C), while calcite melts at a comparatively lower temperature of 1380°F (750°C). Melting a diamond requires specialized equipment and extreme heat, typically achieved through high-temperature flames or lasers. Calcite, on the other hand, can be melted in traditional furnaces or with a focused heat source.

Due to the significant difference in melting points, it is not practical or feasible to melt a diamond and physically mix it with molten calcite. Such an attempt would result in the calcite completely melting while the diamond remains mostly unaffected, potentially with only a slight softening at the edges due to the intense heat.

However, if you are referring to a process known as "mineral melting" or "fusion," where minerals are mixed and heated to extremely high temperatures to form new materials, then it is possible to synthesize new compounds that contain both diamond and calcite components. This process requires sophisticated laboratory equipment and specialized techniques. The resulting materials may have properties and characteristics different from both diamond and calcite alone.