This bizarre and highly aesthetic mineral specimen comes from a new find in Mexico which hit the market in 2017 and started to appear in the hands of fine mineral dealers at the Denver show in September. The specimen consists of many different generations of calcite. The white inner crystals are a very soft, chalky form of calcite - the exact composition is still being debated in mineralogical circles. On top of that is a thin, translucent, harder layer of calcite, and on that is a black layer which appears to be calcite mixed with some other mineral giving it the black, almost bituminous appearance. Coating the outer shell is a glassy, transparent layer of calcite with large crystals.
This particular specimen was the best one shown at the Denver Show, so we acquired it immediately. Most of the specimens from this find have obvious damage and poor aesthetics, but this one is essentialy perfect. Not only is the condition perfect, but the size and aesthetics are outstanding! An extra bonus is the the crystal on the left side is twinned.
It's hard to imagine how a specimen like this could have grown in such a way that the inner core remained exposed while additional generations of crystallization occurred only on the back side. This is really one of the most unique calcite specimens we've ever seen.