It varies depending on the quality of the coal.
Obsidian typically has a smooth, glassy texture due to its quick cooling process when formed from volcanic lava. It has a conchoidal fracture pattern, which means it breaks with curved, shell-like shapes. The grain shape of obsidian is generally fine-grained due to its rapid cooling.
Grain shape.
Sandstone - grain: fine, color: varies (usually tan or brown), texture: rough and grainy, hardness: 6-7 on the Mohs scale. Granite - grain: coarse, color: various (commonly pink, white, or gray), texture: interlocking crystals, hardness: 6-7 on the Mohs scale. Diamond - grain: none (crystalline structure), color: varies (usually colorless), texture: smooth and shiny, hardness: 10 on the Mohs scale.
texture
Grain size typically increases by a factor of 2-4 for each texture category. For example, from fine to medium grain size, there is a doubling or quadrupling of grain size. This progression helps geologists classify rocks based on their crystal sizes.
Anthracite is a form of coal. It is hard black and shiny.
Anthracite is a form of coal. It is hard black and shiny.
Anthracite coal has a hard and brittle texture. It is the highest ranking type of coal and is known for its high carbon content and low moisture content.
Bituminous coal has a smooth texture with a dark color. Its grain is typically fine to medium and can range from a banded appearance due to layering of different materials, to a more homogeneous structure.
Gneiss which is a non-foliated meta-igneous rock is coarse grained in texture.
fined grain texture
The combination of shapes and sizes of grains in a material is known as its grain structure. This grain structure can vary depending on the type of material and the processing techniques used. It can influence the material's mechanical properties, such as strength, ductility, and toughness.
Obsidian typically has a smooth, glassy texture due to its quick cooling process when formed from volcanic lava. It has a conchoidal fracture pattern, which means it breaks with curved, shell-like shapes. The grain shape of obsidian is generally fine-grained due to its rapid cooling.
Grain
Grain
Grain shape.
Sandstone - grain: fine, color: varies (usually tan or brown), texture: rough and grainy, hardness: 6-7 on the Mohs scale. Granite - grain: coarse, color: various (commonly pink, white, or gray), texture: interlocking crystals, hardness: 6-7 on the Mohs scale. Diamond - grain: none (crystalline structure), color: varies (usually colorless), texture: smooth and shiny, hardness: 10 on the Mohs scale.