Quarry tiles are fired clay tiles available in several colours. They are usually quite thick, (1/2 in to 3/4 in, and some even at 1in), and are hardwearing. Because the tiles are self-coloured, (i.e., the same colour all the way through), they show little evidence of wear over time. If you've seen house entrance hallways with a Victorian mosaic-type tiled design in different colours, these tiles have been produced in the same way.
There's still one manufacturer in the UK, and their website is
here.