Coal is classified into four main types or ranks, primarily based on the degree of coalification — the process of transformation from plant material to coal under heat and pressure over geological time. 1. Anthracite Coal Carbon Content: 86% to 97% (highest among coal types) Appearance: Hard, shiny, black coal with a glossy luster Energy Content: Very high calorific value Properties: Burns cleanly with very little smoke or soot Uses: Primarily used for residential and commercial heating; also used in metallurgical processes where a high carbon content is required. Occurrence: Less abundant and found in limited locations worldwide. 2. Bituminous Coal Carbon Content: 45% to 86% Appearance: Dense, black coal, dull or shiny, softer than anthracite Energy Content: High calorific value, widely used for energy Properties: Contains volatile matter; produces more smoke and soot compared to anthracite Uses: The most widely used coal type; fuel for electricity generation, industrial boilers, and steel production (coking coal variant). Occurrence: The most abundant coal type globally. 3. Sub-bituminous Coal Carbon Content: 35% to 45% Appearance: Black to dull black coal with relatively low moisture content Energy Content: Lower than bituminous coal but still significant Properties: Lower sulfur content, cleaner-burning than bituminous coal Uses: Mainly used for electricity generation in power plants; often preferred for its cleaner emissions compared to bituminous coal. Occurrence: Found in many coal reserves, often younger geologically. 4. Lignite Coal (Brown Coal) Carbon Content: 25% to 35% (lowest rank coal) Appearance: Brownish-black, soft, crumbly coal with high moisture content Energy Content: Lowest calorific value among coal types Properties: High moisture content reduces efficiency; burns with a lot of smoke Uses: Mainly used in electricity generation close to mining sites due to low energy density and high transport costs. Occurrence: Most abundant coal type; often surface mined.