For several years in the 1950s and 1960s, a by-product of the potassium production called Alkarb was a main source for rubidium.
fɔːɹ sˈɛvɹəl jˈɪɹz ɪnðə nˈaɪntiːnhˈʌndɹɪd fˈɪfti z ænd nˈaɪntiːnhˈʌndɹɪd sˈɪksti z, ɐ baɪpɹˈɑːdʌkt ʌvðə pətˈæsiəm pɹədˈʌkʃən kˈɔːld ˈælkɑːɹb wʌzɐ mˈeɪn sˈoːɹs fɔːɹ ɹuːbˈɪdiəm.