Here's why:

* Very hard rock: Anthracite is the hardest form of coal, with a Mohs hardness of 2.5-3.5.

* Burns with high heat and smoke: Anthracite is a high-grade coal with a high carbon content, making it burn very hot and produce less smoke than lower-grade coals.

* Metamorphic formed from coal: Anthracite is formed from bituminous coal through intense heat and pressure deep underground. This process transforms the coal's structure and increases its carbon content.

Let me know if you have any other questions about rocks or minerals!