Rhodocrosite is, in general, a low temperature hydrothermal mineral but in veins and fumeroles can be deposited at moderate to high temperatures. It is a common occurrence with silver deposits. As a member of the calcite group of minerals, Ca and Fe can substitute in the place of Mn forming a number of solid solutions; Mg, Zn, and Co can also occur in the place of Mn.
The “Emperor” is from the Wudong Mine in China, a retired lead mine that is a source of collector’s minerals including fluorite, pyrite, molybdenite, and sphalerite. The host rocks are Cambrian cherts, siltstones, and shales. Several periods of faulting were accompanied by hydrothermal mineralization including lead, zinc, fluorite, manganese and silver at temperatures ranging from 100C to 300C. The lovely rose-like blades in this sample are due to its inherent crystal lattice symmetry (trigonal, like calcite) and extended growth in a fluid-rich environment.
Most rhodocrosite one stumbles over in the field is not nearly as pretty as the Emperor of China, but it is nearly always pink.
More mineral information on rhodocrosite