Finally, oil sands are a mixture of clay, sand, water, and bitumen ... Like modern-day alchemists, they are looking for a way to turn rock into oil. The promise of oil shale has been tantalizing ...

It is often found in organic-rich shale and thin interlayers of carbonate rocks, sandstones and siltstones ... lower maturity and higher clay content, making its development extremely challenging ...

As an example, expanded shale, clay and slate (ESCS) lightweight aggregates are fired in rotary kilns and so represent a significant amount of embodied energy and greenhouse gas emissions.