From the type locality, the San Venanzo quarry, this exceedingly rare hydrated, potassium, calcium, alumino silicate is a member of the zeolite group of minerals. Emplaced in a boxwork matrix are spherical aggregates of lustrous and translucent, white to cream colored willhendersonite crystals - but they are micros, and you won't see them in this photo. Ex. Renato Pagano collection to William "Bill" Henderson, in a trade long ago. I obtained this when I bought Henderson's well known Micro collection (donated now to the RRUFF project). This is an important specimen for the size, and the provenance of two very well known and respected collectors of rarities.