63 Europium -Eu- Its compounds are widely used in phosphors for cathode ray TV screens and in compact fluorescent bulbs. Pure crystals like this are useful only as a source of europium to be turned into compounds.
66 Dysprosium -Dy- its highly susceptible to magnetization, it is employed in various data storage applications, such as in hard disks. Dysprosium powder may present an explosion hazard when mixed with air and when an ignition source is present. Thin foils of the substance can also be ignited by sparks or by static electricity. Dysprosium fires can't be put out by water.
55 Cesium -Cs- The cesium in this ampoule melts if you hold it in your hand for a minute, yielding the prettiest liquid gold. If the ampoule were to break in your hand, the resulting explosion would be extremely unpleasant.
Elbaite, on Quartz, nicknamed "Rabbit Ears". Amazing natural crystal formation ~ Houston Museum of Natural Science, Cullen Hall of Gems and Minerals (photo credit: Houston Convention and Visitor's Bureau)