This is a massive and well formed cluster from this famous and epic find from Palmarejo. Almost the entire find was composed of rare fishtail twins of calcite that had at least seven generations of growth.
Less spoken about is how the rare secondary minerals played a big role in the unique formations of the find. 
Romancheite, which composes what most people are familiar with as Psilomelane (the black mineral included in the edge of the calcite generations, propagated growth between generations and changed crystallography). 
Palygorskite, known more by people as “mountain leather” and has a chemical formula that looks like the product of someone trying to drown a a Sapphire (the white coating, which halted any further calcite growth on the isolated surface it exists on).
Chalchophanite, a mineral literally named for how it changes color when you light it on fire (the black mineral that’s on the outside of the calcite).
Calcite, Romancheite, Palygorskite, and Chalcophanite - Palmarejo Mine, Chihuahua, Mexico. 
18.7 x 17.4 x 13.4 cm.