Glauconite is the group mineral name that is contained in "Greensand". Its nomenclature was most recenly defined in the API Handbook of GEology , (which got its insert from Bailey, S. W. 1980, THE HANDBOOK OF CLAY AND CLAY MINERALS
glauconite sands are mined in Delaware and NEw Jersey and in the coastal plain of MAssachussetts and Maine and New Hampshire. Chemical companies used to use glauconite as the model fro developing new ion exchange salts and resins . Its still used extensively in packing towers for municipal water supplies. (Usually they have 2 towers and they dont backwash, they rebbed the towers one at a time while they watch for breakthrough for iron and manganese. They will take the old greensand back and extract the exchanged ions.(They used to use it for packed beds to collect gold and platinum in water out west. The greensand was mixed with Rohm and Haas ion exchange resins.
Its neat stuff