 Although europium is present in most of the minerals containing the other rare elements , due to the difficulties in separating the elements it was not until the late 1800s that the element was isolated . William Crookes observed the phosphorescent spectra of the rare elements and observed spectral lines later assigned to europium . 
 Although europium <a href='drop_aux' title='1'><mark>is</mark></a>present in most of the minerals containing the other rare elements , due to the difficulties in separating the elements it <a href='negative_concord' title='2'><mark>was</mark></a> <a href='negative_concord' title='3'><mark>not</mark></a>until the late 1800s that the element was isolated . William Crookes observed the phosphorescent spectra of the rare elements and observed spectral lines later assigned to europium . 
Although europium present in most of da minerals containing tdaother rare elements , due to the difficulties in separating thdalements it ain't until the late 1800s that the element was isolated . William Crookes observed the phosphorescent spectra of thedare elements and observed spectral lines later assigned to europium .