I had two hits when I did a couple of Google searches...

The first hit I got was an Oprah's Book Club novel, "Stolen Lives: Twenty Years in a Desert Jail" by Malika Oufkir (on sale for $0.01 on Amazon if anyone's interested). 

The other one I found (and I think is the one you're looking for) is "The Crescent" by Chris Merle. The synopsis mentions an escape from a Saudi mental hospital, which might be confused for a prison, and talks of finding desert diamonds during an escape. The cover is red and black, but features a crescent moon rather than a diamond. 

Good luck on the search and hope this helped!

On Wed, Jun 22, 2016 at 12:00 PM, Diane Willick <dwillick@ruthhughes.org> wrote:
I have a stumper.  Patron came in looking for a book and i have no ideas. She says that it is a black cover with a red diamond on the front. It is about a man that has been in prison and he escapes.  He crawled across the desert and on the way finds a bunch of diamonds.  They were all inherited by his family.  The story is told by one of his twin sisters. HELP!!  It does not ring any bells in my belfry. A fiction work.  Thank you.

Diane Willick
Ruth Hughes Memorial District Library

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