From the CRC handbook of Chemistry and Physics, CRC Press, Cleveland,  55th ed., 1974-75 "The Elements" by C.R. Hammond. page B-34
THULIUM (Thule, the earliest name for Scandinavia), Tm; at. wt.  168.9342; at. no. 69; m.p. 1545 +/- 15 C; b.p. 1947 C; sp.gr. 9.321 (25 C); valence 2,3.  Discovered in 1879 by Cleve.  Thulium occurs in small quantities along with other rare earths in a number of minerals.  It is obtained  commericially from monazite, which contains about 0.007% of the element. Thulium is the least abundant of the rare-earth elements, but with new sources recently discovered, it is now considered to be about as rare as silver, gold, or cadmium.  Ion-exchange and solvent extraction techniques have  recently permitted much easier separation of the rare earths, with much  lower costs.  Thulium metal, only a few years ago, was not obtainable at any cost; in 1849 the oxide sold for $450/gm.  Thulium metla now costs from $3 to $20/gm. depending on the purity, quantity, and supplier.  Thulium can be isolated by reduction of th eoxide with lanthanum metla or by calcium  reduction of the anhydrous fluoride.  THe pure metal has a bright, silvery luster.  It is reasonably stable in air, but the metal should be protected from moisture in a closed container.  The element is hard, silver-gray, soft, malleable and ductile, and can be cut with a knife.  Sixteen isotopes are  known, with atomic masses ranging from 161 to 176.  Natural thulium, Tm(168), is stable.  Because of the reatively high price of the mteal, thulium has  not yet found many practical applications.  Tm(169) bombarded in a nuclear reactor can be used as a radiation source in portable x-ray equipment.   Tm(171) is potentially useful as an energy source.  Natural thulium also  has possible use in ferrites (ceramic magnetic materials) use d in microwave equipment.  As with other lanthanides, thulium has a low to moderate acute toxic rating.  It should be handled with care.