Others remember an efficient administrator (admittedly, a rare and valuable species in Russia), always polite, but with no feel for bigger questions.

ECONOMIST: Russia��s Putin puzzle

So, today, you all have a rare and valuable chance to pursue your own passions, chase your own dreams without incurring a mountain of debt.

WHITEHOUSE: President Obama Gives Commencement Address at Kalamazoo Central High School | The White House

"Being hand-written would have made it rare and valuable even when it was new, so it is not a surprise to find it shows signs of marks from the copper clasps which held its chains when it was in the nun's library, " he said.

BBC: Lacock Abbey displays 14th Century bible 'dictionary'

Some materials in solar modules such as silicon and rare metals could be more valuable in the future, providing an additional incentive to recycle.

FORBES: Rare Earth Recycling: A Key to the New Energy Economy

That makes them more rare and, in turn, more valuable.

FORBES: Why 756 Will Not Equal Millions

"The opportunity to learn from such a hugely successful and experienced film-maker is very rare indeed, and I have no doubt that it will be a valuable one, " she said.

BBC: Mark Andrews

Soliris is very valuable in treating two conditions: a rare form of anemia and an even rarer kidney ailment known as atypical hemolytic uremic syndrome.

FORBES: What Is The Rationale For The Pricing Of New Drugs?

The two superpowers are competing over a valuable new resource -- the rare earth elements used in the construction of nearly all smartphones, tablets and other electronic gadgets.

CNN: The future world of 'Call of Duty: Black Ops II'