This is a question similar to A word to describe something that is desired only because it is rare, but I am looking for an expression, a saying, or an idiom use in daily life, not a term or jargon.
I'm also err on the side of natural (not artificial) rareness, and the thing is truly valuable. Something like "diamond is precious because it's rare".
Best Answer
precious few ; precious little*
Its colloquial usage is merely to describe something that there is very little of, but that doesn't mean it hasn't been used in contexts of something actually being precious just through its rarity. Such examples are outlined here:
Sermons, homiletical expositions, and leading thoughts on texts of Scripture
Life Lessons: Train of Thought
Marnie's Christmas Wish
31 SINS: AN ANTHOLOGY
...And hundreds of other instances can be found on Google Books:
--Used to describe endangered species:
--Used to describe rare jewels:
--Used to describe rare/unique moments:
*(btw, precious few should be preferred over precious little in this particular usage because little will make the reader misread the object in question as small, and not rare.)
The connotative advantage of few in its relation to precious is that few usually means only a handful, or from any small number above two. For this reason, few connotes a greater rarity than even rare itself does. For example, a rare species could number anywhere from the hundreds to the thousands, but a species that there is few of would only number from the tens to the hundreds, which makes its use an example of litotes, or understatement/underestimate for persuasive effect.