Cynthia Pelman 
The Voice of the Xenolith [EPUB ebook] 

Thirteen-year-old Amethyst does not get on with her teachers. Her classmates think she is weird. She prefers to be on her own, and she wishes she did not have to go to school. Amethyst reads detective stories, collects fossils, loves archaeology, and is writing her own dictionary. She has trained herself to become an expert in tracking, searching and following clues, and she uses these detective skills to search for someone who was murdered seventy years ago. Amethyst reaches out across time and space and in doing so finds her own voice among the many meanings of silence.