Geology — Igneous, Sedimentary and Metamorphic Rocks
Learn to tell apart the three main rock types (igneous, sedimentary and metamorphic), how they form and how minerals differ, with practice adapted to Primary and Secondary. The Diagnosis makes you reason by elimination until you identify each rock from its clues.
Geology · Primary, Secondary
Igneous (from cooling magma or lava), sedimentary (build-up of remains and particles) and metamorphic (heat and pressure on another rock). Knowing which group each belongs to is the foundation of the topic.
Granite and basalt cool from magma; limestone and sandstone form on the seafloor or by compaction; marble and slate arise through metamorphism. Each origin leaves visible clues.
A mineral (like quartz) is a pure substance with its own composition; a rock is usually a mixture of minerals. Telling the two apart is a common mistake the Diagnosis helps to fix.
"A Secondary student kept confusing marble with an igneous rock. After several Diagnosis rounds reasoning through the clues (it forms from limestone under heat and pressure), they linked marble to metamorphic rock for good."
Tricks and techniques to master this topic faster:
Igneous comes from 'ignis', fire: it comes from magma or lava. Large crystals mean slow cooling (granite); tiny ones mean fast cooling (basalt).
Sedimentary = sediments: it forms layer by layer. Many have visible fossils or grains (sandstone, limestone).
Metamorphic = 'metamorphosis', change: another rock transformed by heat and pressure. Limestone becomes marble; clay becomes slate.
Quartz is a mineral, not a rock: it's one of the hardest and most common in the Earth's crust.
If you are studying Rocks and Minerals — Types and Formation, these curriculum topics complement each other:
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