Bornite is a copper iron sulfide, and at this rich mine in Zacatecas, it is an important ore that sometimes had thin fissures that were sometimes found with these veins or leafs of native silver filling them. Here, the silver leaf has been excavated so that it stands up dramatically off the iridescent bornite that served as host, creating quite a dazzling specimen of native silver, from a classic Mexican locality. The silver leaf here measures over 6 cm from end to end. Ex. Martin Zinn Collection.