Which rock is known to be the hardest to drill?

Quartzite is recognized as one of the hardest rocks to drill due to its composition and formation process. It is primarily composed of quartz grains that have been tightly fused together under high heat and pressure, resulting in a very dense and durable rock. This extreme hardness makes it particularly challenging for drilling equipment, which can struggle to penetrate the tightly packed grains effectively.

While granite is also known for its hardness and can present challenges during drilling, it is not as difficult to penetrate as quartzite. Marble, while it has a certain level of hardness, is generally softer compared to quartzite and granite. Conglomerate contains rounded pebbles that make drilling easier in comparison to solid, uniformly hard rocks like quartzite. Understanding the properties and physical structure of these rocks emphasizes why quartzite is identified as the hardest to drill in this context.