This is a highly unusual specimen of yellow prehnite in the form of sharp, bladed crystals forming a larger cluster. I have not seen prehnite like this from Merelani, although some of the blue-ish crystals found in 2010-2011 and misidentified initially as albite come close. The piece is dramatic, and has prehnite of a significant size for the species. I bought this from a photo on the hunch it might actually be a new species or something weird, and it was analyzed at the University of Arizona to be 100% sure it is, indeed, prehnite. As far as miniature prehnites with giant crystals go, it is nearly in a class of its own.