Note the overall color. Use terms like leucocratic (light-colored/felsic), mesocratic (medium), or melanocratic (dark-colored/mafic).
Distinguish between the fresh surface (broken with a hammer) and the weathered surface . Weathering can hide the rock's true color or highlight certain mineral textures. 2. Texture (The Cooling History) Texture is the most critical diagnostic feature: The Field Description of Igneous Rocks
If porphyritic, describe the shape, color, and size of the large crystals specifically. 4. Fabric and Structure Look for patterns in how the rock is arranged: Massive: Uniform throughout with no preferred orientation. Note the overall color
Large crystals ( phenocrysts ) set in a fine-grained groundmass (indicates a two-stage cooling process). Weathering can hide the rock's true color or
Look for xenoliths (pieces of "foreign" country rock caught in the magma). 5. Field Relationships Observe how the rock body relates to its surroundings:
No crystals (extremely rapid quenching, like obsidian). Vesicular: Contains gas bubbles (common in lavas).
Identify the primary minerals (e.g., Quartz, Feldspar, Olivine, Pyroxene).