I remember, when I was in middle school, reading a series of mystery books. The titles were of the format 'X and Y', where X was a type of gemstone, and X and Y began with the same letter.
As far as more specific details, I'm afraid I don't remember much.
- The only language I've ever been fluent in is English. I highly suspect the books were originally written in English, but I know for sure they are at least available in English.
- The reading level of the series is likely aimed somewhere between 5th and 9th grade reading levels (roughly 11 to 15 years old).
- I know that there were at least 4 books in the series (likely more).
- The entire series takes place on earth (no sci-fi or fantasy components)
- There are multiple protagonists, including at least one male and at least one female.
- One of the novels included a plot point of ceramic guns, such that they made it through airport security
- Another plot point (possibly in the same book, possibly in another) involved a statue (Jade, IIRC), with a tracking device that was one of the eyes of the statue itself.
- I was in middle school in Utah (United States) in the late 1990's / early 2000's.
- I'm 90% sure (though not 100%) that the author (or at least the pseudonym) was female.