* Alternating layers of dark and light colors: This suggests a layered intrusion of magma, where different mineral compositions solidify at different rates. Darker minerals (like pyroxene or amphibole) tend to crystallize first, followed by lighter minerals (like quartz or feldspar).
* Visible quartz crystals: Quartz is a common mineral in igneous rocks. The presence of visible crystals indicates slow cooling, which allows for larger crystals to form.
* No fossils: Fossils form in sedimentary rocks, which are made from the accumulation of sediments and organic matter. Igneous rocks form from the cooling and solidification of molten rock, so they cannot contain fossils.
Examples:
* Diorite: A common intrusive igneous rock with alternating layers of dark and light minerals.
* Gabbro: Another intrusive igneous rock with a similar layered appearance.
In contrast:
* Sedimentary rocks typically form in layers, but these layers are made up of sediments, not minerals crystallized from magma.
* Metamorphic rocks are formed from existing rocks that are changed by heat and pressure, and they may show signs of their original formation (e.g., layers, fossils).
