If a Na+ ion substitutes for a Ca+2 ion, it creates an unequal charge that must be balanced by other ionic substitutions elsewhere in the crystal. Feldspars, micas, and ferromagnesian minerals (pyroxenes, amphiboles, olivines, etc.) If magma cools slowly, deep within the crust, the resulting rock is called intrusive or plutonic. All of the sheet silicate minerals also have water molecules within their structure. Another is the native rock is melted and consumed into the rising magma or broken into pieces that settle into the magma, a process known as stoping. Note how the mineral accommodates the substitution of Ca++ and Na+. The hardness and lack of cleavage in quartz result from the strong bonds characteristic of the silica tetrahedron. To help you keep the sili names straight, here is a summary table: In silicate minerals, these tetrahedra are arranged and linked together in a variety of ways, from single units to complex frameworks (Table 3.2). This page titled 4.1: Classification of Igneous Rocks is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & Cam Mosher (OpenGeology) . The result is that the oxygen-to-silicon ratio is lower than in olivine (3:1 instead of 4:1), and the net charge per silicon atom is less (2 instead of 4), since fewer cations are necessary to balance that charge. Biotite mica can have iron and/or magnesium in it and that makes it a ferromagnesian silicate mineral (like olivine, pyroxene, and amphibole). Depending on many factors, such as the original magma chemistry, silica-oxygen tetrahedra can combine with other tetrahedra in several different configurations. Mafic rocks often also contain calcium-rich varieties of plagioclase feldspar. Arndt, N. T. Chapter 1 Archean Komatiites. This gives mica its characteristic property of easily cleaving into sheets. If you dont have glue or tape, make a slice along the thin grey line and insert the pointed tab into the slit. All of the ions shown are cations, except for oxygen. It is characteristically green when not weathered. This difference in density ends up being important in controlling the behavior of the igneous rocks that are built from these minerals: whether a tectonic plate subducts or not is largely governed by the density of its rocks, which are in turn controlled by the density of the minerals that comprise them. Biotite mica can have iron and/or magnesium in it and that makes it a ferromagnesian silicate mineral (like olivine, pyroxene, and amphibole). Clays In pyroxene, silica tetrahedra are linked together in a single chain, where one oxygen ion from each tetrahedron is shared with the adjacent tetrahedron, hence there are fewer oxygens in the structure. Lab 2: Mineral Properties and Non-Silicate Minerals, Lab 6: Metamorphic Rocks and the Rock Cycle, Lab 7: Relative Dating and Geological Time, A Practical Guide to Introductory Geology, Creative Commons Attribution 4.0 International License, A crystal of pure silicon sliced very thinly and used for electronics, A combination of one silicon atom and four oxygen atoms that form a tetrahedron, The proportion of a rock that is composed of the component SiO, A mineral that contains silica tetrahedra (e.g., quartz, feldspar, mica, olivine), Micas, clay minerals, serpentine, chlorite, One type of pyroxene mineral that you will see in this course is called, One of the most common amphibole minerals is called, Two common minerals from the mica family that you will see in this course are, Three feldspar minerals you will encounter in this course are.
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