GLY 101 1st Edition Lecture 3 Outline of Last Lecture I. Matter and MineralsOutline of Current Lecture II. Igneous CompositionIII.Igneous Textures-texture is used to describe the overall appearance of a rock based on size, shape and arrangement of its mineral grains-different types of textures include:1. glassy texture2. porphyritic texture3. phaneritic texture4.vesicular texture5. pyroclastic texture6.aphanitic textureCurrent LectureII. Igneous Composition- Igneous rocks are mainly composed of silicate minerals-when magma cools and solidifies this forms 2 major groups of silicateminerals: 1. the dark silicates- rich in iron and magnesium, low in silica2.the light silicates- contain greater amounts of potassium, sodium, and calcium rather than iron and magnesium -igneous rocks which quartz and potassium feldspar are dominant minerals have granitic composition.-granitic rocks are felsic -felsic is derived from feldspar and silicaThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-rocks that contain at least 45% dark silicate minerals and calcium rich feldspar, not quartz, have basaltic composition-basaltic contain high percentage of ferromagnesian mineral, this is referred to as mafic-rocks with composition between granitic and basaltic rocks have andesiticcomposition-peridotite contains mostly olivine and pyroxene, its chemical composition is referred to as ultramafic.III. Igneous Texture-texture is used to describe the overall appearance of a rock based on size, shape and arrangement of its mineral grains-different types of textures include:1. glassy texture2. porphyritic texture3. phaneritic texture4.vesicular texture5. pyroclastic texture6.aphanitic textureIV. Naming Igneous Rocks- igneous rocks are classified by their texture and mineral composition-Granite is the best known igneous rocks- rhyolite is the fine-grained equivalent of granite and is composed essentially of light colored silicates -Rhyolite is usually pink to light grey in color-Obsidian is dark-colored glassy rock that usually forms when highly silica-rich lava cools quickly when it hits Earth’s surface.-Pumice is a volcanic rock with a glassy texture-pumice forms when large amounts of gas escape through lavaV. Andestsitic (Intermediate) Igneous rocks-Andesite is a medium-gray, fine grained rock-usually from volcanic origin-commonly exhibits porphyritic texture- diorite is the intrusive equivalent of andesite-diorite has a salt and pepper appearance due to light colored grains and dark colored crystalsVI. Basaltic (mafic) igneous rocks-dark green to black, fine grained rock-basalt is the most common extrusive igneous rock- Gabbro is the intrusive equivalent of basalt- is dark in color like basalt due to pyroxene and calcium-rich plagioclase