The english mineralogist H. J. Brooke named brewsterite after Sir David Brewster the scottish physicist and mathematician in 1822. The brewsterite belongs to the zeolite group, a strontium and barium aluminium silicate mineral. Before 1997 brewsterite was considered as a mineral specie, however the IMA (International Mineralogical Association) changed it to brewsterite series, because the presence and quantity of strontium (Sr) and barium (Ba) is not the same at all pieces. The Sr-brewsterite is more common than the Ba-brewsterite, but almost always consists barium. Their crystals formed with a hydrothermal method, usually in the cavities of volcanic rocks (basalt). They issue in little prismatic columns, sometimes twinned. In one of its best locations, in the Strontian mines, Scotland the brewsterite crystals are often followed by calcite, harmotome and galena crystals. Localities: Scotland, Germany, Norway, Canada, USA etc.