Anthracite, the highest rank of coal, is formed through a long and complex process involving intense heat and pressure over millions of years. Here's a breakdown of how it happens:

1. Formation of Peat: It all starts with the accumulation of plant matter, primarily in swampy environments with abundant water and limited oxygen. As the plant material dies, it partially decomposes, forming a soft, spongy substance called peat.

2. Burial and Compaction: Over time, layers of sediment, such as mud and sand, bury the peat deposits. The weight of these layers compresses the peat, squeezing out water and air. This compaction significantly increases the density and carbon content of the material.

3. Heat and Pressure: As the sediment layers continue to build up, the pressure on the buried peat intensifies. The Earth's internal heat also plays a role, gradually increasing the temperature within the layers.

4. Metamorphism: Under these extreme conditions of heat and pressure, the peat undergoes a process called metamorphism. This transforms the peat into coal, progressively increasing its rank as the process continues.

5. Anthracite Formation: The final stage of metamorphism occurs when the buried peat is exposed to temperatures exceeding 200°C (392°F) and pressures exceeding 1,000 atmospheres. These conditions result in the formation of anthracite, the hardest and most carbon-rich type of coal.

Key Characteristics of Anthracite Formation:

* High Carbon Content: Anthracite has the highest carbon content of all coal types (over 90%).

* Low Moisture Content: Anthracite contains very little moisture due to the intense pressure and heat it experiences.

* High Energy Content: Because of its high carbon content, anthracite burns hotter and produces more energy than other coal types.

* Shiny and Hard: Anthracite is characterized by its shiny, black surface and its hardness.

Note: Anthracite formation is a very slow process that can take millions of years. The exact conditions and duration required for anthracite formation can vary depending on the specific geological environment.