What is the Japanese word for Diamond?

Also if this person had a sister and there parents wanted to keep a
jewel/gem them what would be a good name?

This question is asked to help me with part of my Beat of Defiance II fanfic
(chapter  4 is done, but I want to fill in the names as it was.

Thanks
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Ben L. Harrison - HM1(FMF)/USN/RET
Harriso3@ix.netcom.com
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Anime Excuse #212: Went  on a  mission with the  Lovely Angels
Anime Excuse #213: Tried to help Linna start her car