Have you read any of the Geology threads by karin_mt? She lists several simple tests you can do to test the slabs you are considering and understanding their properties before you spend your money.

Can you get a small chunk from one of the slabs so you can test at home? If not, you can still do a few key tests right at the slab yard.

Many of the slabs labeled as a quartzite are really marble, so buyer beware.