Lanthanum Element Number 57 La 

Three rather large chunks of Lanthanum metal, these were once silvery but Oxides have formed on the material. I keep these in oil, and the metal still oxidizes, it is very reactive. 

 La 57 Lanthanide AW: 138.90547  D:.94  MP: 1688  BP: 6267c  Mohs:2.5

Lanthanum is the first official element  of the Lanthanide series. Lanthanum is a grayish silver metal which Oxidizes rapidly in air to form a heavy Oxide, If left in the air long enough, this metal turns into a powder. I keep my Lanthanum samples under paraffin oil.

Lanthanum is a silvery metal, when not oxidized, and is relatively malleable. Like most rare earth metals, its primary source is monazite.The US has a vast resource of monazite, but conflict with the Florida tourism industry over the beach sand gets in the way.

Lanthanum has a few important uses, lanthanum is used in hybrid car batteries that have over 20 pounds of this metal. Mischmetal used in lighters as a flint. optics, and scintillator photon  detectors. Lanthanum is used in medicine, to treat renal failure. Lantern mantles and welding rods, both in applications similar to Thorium. Alloys with steel and other metals like Molybdenum. Even phosphors can be made with Europium and Lanthanum, the list goes on.

Like many rare earth metals Lanthanum is difficult to extract and purify. Many steps must be taken to bring monazite to rare earth metals, and usually the end process of ion exchange will produce the final products. Lanthanum is relatively inexpensive rare earth metal.

A quick word on the rare earth elements, also known as Lanthanides. Most of these elements can be extracted from monazite, and most have similar traits. The term rare earth is misleading, because many commonly known elements are rarer, for example Iodine is less abundant than Thulium. The term rare earth metals was most likely due to the extraction difficulties back in the day. Lanthanides generally form trivalent compounds,  Europium can form Eu II and Eu III compounds.

Cerium Element Number 58 Ce 

Cerium is the second Lanthanide metal, and is a reactive silvery metal. Like Lanthanum, I keep my Cerium under paraffin oil. Cerium has many industrial uses, one important use is as a glass polish for optical lenses.

Cerium can be used in catalysts, glass additives, glass polishes, alloys, pigments, and medicines. Cerium also can be used in gas light mantles,sorta like Thorium and welding applications. I have a Cerium doped Yttrium Aluminum Garnet gem stone that has a bright glow in both long and short wave UV light.

Cerium can ignite in higher temperatures in air, and like many reactive metals, this element can liberate and ignite Hydrogen from water, so a Cerium fire is very dangerous and toxic.

Cerium has 4 stable isotopes and 26 radio isotopes. One radio isotope Cerium144 which is a reactor byproduct is used in thermoelectric radioisotope generators.  

Cerium is yet another reactive lanthanide metal. These two chunks of pure Cerium look like rocks, and are kept under oil.

Ce 58 Lanthanide AW:140.116  D:6.77  MP:1463  BP:6229  Mohs 2.5

 This YAG  crystal is Cerium doped, and was created for photon counters, and very sensitive radiation detectors.

This crystal glows under both short and long wave ultra violet light.