Question
This process is responsible for the amorphous structure and green color of the rare gemstone ekanite. For 10 points each:
[10h] Name this process that forms spherical regions of discoloration called pleochroic halos and causes the partial or complete destruction of crystal structure through metamictization.
ANSWER: radioactive decay [or radioactivity; accept word forms; or alpha decay; reject other specific types of radioactive decay]
[10m] Zircons are highly variable because of pleochroic halos and metamictization due to the high amounts of these two elements. The decays of these two elements to lead are used to date long-time scales, as besides bismuth, they are the only primordial radioactive elements.
ANSWER: thorium and uranium [or Th and U; accept in either order]
[10e] Thorium is mainly a byproduct of processing ores of these elements, such as monazite. Thorium and uranium often occur along with this set of chemically similar elements because they are the lighter analogs of the actinides.
ANSWER: lanthanides [prompt on rare earths, rare-earth elements, or rare-earth metals]
<Gerhardt Hinkle, Chemistry>
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