ESS105H1 Lecture 4:
Document Summary
These rocks from when magma cools and solidifies. There are two types of ir: extrusive (volcanic): ir that forms when magma solidifies at the earth"s surface (e. g. basalt, intrusive (plutonic): ir that forms when magma solidifies underground (e. g. granite) Intrusive igneous rocks cool slowly deep beneath earth"s surface and are typically coarse-grained - this texture is referred to as phaneritic. Glassy texture = no crystals: formed from cooling so quickly crystals do not even have time to form; typically form in some volcanic rock. A pegmatite is an extremely coarse-grained igneous rock formed as the last bit of granitic magma cools slowly at depth. A porphyritic texture includes two distinct crystal sizes, with the larger having formed first during slow cooling underground and the smaller forming during more rapid cooling at the earth"s surface. Pyroclastic texture is composed of volcanic ash and larger solid fragments that erupted from volcano.
